diff --git a/.circleci/config.yml b/.circleci/config.yml
index 06704f9..fbf3d05 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -12,8 +12,8 @@ aliases: &build
     - checkout
 
     - run:
-        name: create a fake /nix
-        command: sudo mkdir -m 0755 /nix && sudo chown circleci /nix
+        name: create a fake /nix, enable single-user install of nix as user circleci
+        command: sudo mkdir -m 0777 /nix && sudo chown -R circleci /nix
 
     # Restore the nix installation to its state after the previous test run.
     # This should prevent unnecessary rebuilds of dependencies without impacting
@@ -31,17 +31,17 @@ aliases: &build
         name: install nix
         command: |
           [[ -d ~/.nix-defexpr ]] ||
-          curl https://nixos.org/nix/install | sh
+          curl https://nixos.org/releases/nix/nix-2.2.1/install | sh
 
     - run:
         name: install nix dependencies used in the test script itself
         command: |
           nix-env -i cabal2nix
-          nix-env -i nix-prefetch-git
+          nix-env -i nix-prefetch-scripts
 
     - run:
-        name: run the tests (temporarily - just build to reset the cache)
-        command: nix-build --show-trace build.nix
+        name: run the tests
+        command: nix-shell --run 'cabal new-test haskell-overridez-tests'
 
     # Save /nix and the nix user folders to the cache.
 
diff --git a/.gitignore b/.gitignore
index 69e79fe..05aae81 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,5 +1,5 @@
 # haskell development
-result
+result*
 .ghc*
 dist
 dist-newstyle
diff --git a/.travis.yml b/.travis.yml
new file mode 100644
index 0000000..e795787
--- /dev/null
+++ b/.travis.yml
@@ -0,0 +1,3 @@
+language: nix
+nix: 2.2.1
+script: nix-shell --run 'cabal new-test haskell-overridez-tests'
diff --git a/build.nix b/build.nix
index 9455420..4271abc 100644
--- a/build.nix
+++ b/build.nix
@@ -28,4 +28,5 @@ in
 pkgsMake pkgsMakeArgs ({ call, lib, ... }: rec {
   haskell-overridez-exe = call.haskell.cabal2nix.app ./.;
   haskell-overridez = call.package ./nix/wrapper;
+  haskell-overridez-tests = call.haskell.cabal2nix.lib ./haskell-overridez-tests;
 })
diff --git a/cabal.project b/cabal.project
new file mode 100644
index 0000000..38e4736
--- /dev/null
+++ b/cabal.project
@@ -0,0 +1,3 @@
+packages:
+  ./
+  ./haskell-overridez-tests
diff --git a/fixtures/gobanme-no-yagai-purojekuto/.gitignore b/fixtures/gobanme-no-yagai-purojekuto/.gitignore
deleted file mode 100644
index 81259c4..0000000
--- a/fixtures/gobanme-no-yagai-purojekuto/.gitignore
+++ /dev/null
@@ -1 +0,0 @@
-nix
diff --git a/fixtures/gobanme-no-yagai-purojekuto/DESC b/fixtures/gobanme-no-yagai-purojekuto/DESC
deleted file mode 100644
index 81b768f..0000000
--- a/fixtures/gobanme-no-yagai-purojekuto/DESC
+++ /dev/null
@@ -1 +0,0 @@
-create an overlay from config fetched from a subpath of a github repository
diff --git a/fixtures/gobanme-no-yagai-purojekuto/Main.hs b/fixtures/gobanme-no-yagai-purojekuto/Main.hs
deleted file mode 100644
index e335da6..0000000
--- a/fixtures/gobanme-no-yagai-purojekuto/Main.hs
+++ /dev/null
@@ -1,8 +0,0 @@
-{-# LANGUAGE OverloadedStrings #-}
-
-module Main where
-
-import Turtle
-
-main :: IO ()
-main = echo "Hello, world!"
diff --git a/fixtures/gobanme-no-yagai-purojekuto/default.nix b/fixtures/gobanme-no-yagai-purojekuto/default.nix
deleted file mode 100644
index 00dcfa5..0000000
--- a/fixtures/gobanme-no-yagai-purojekuto/default.nix
+++ /dev/null
@@ -1,26 +0,0 @@
-let
-  overridez = import ./nix/haskell-overridez.nix;
-  githubKara = overridez.allIn ./nix/github.com/adetokunbo/example-fetched-haskell-overridez/subdir-root/a-subdir;
-  overlays =
-    let dropTestPkgs = haskellPackagesNew: haskellPackagesOld: {
-            foldl = null;
-            managed = null;
-            optparse-applicative = null;
-            turtle = null;
-            gobanme-no-yagai-purojekuto = haskellPackagesNew.callPackage ./nix/gobanme-no-yagai-purojekuto.nix {};
-          };
-    in [
-      (newPkgs: oldPkgs:
-         let
-           inherit (oldPkgs.lib) composeExtensions fold;
-           composeExtensionsList = fold composeExtensions (_: _: {});
-         in {
-           haskellPackages = oldPkgs.haskellPackages.override {
-             overrides = composeExtensionsList [dropTestPkgs (overridez.combineAllIn ./nix [githubKara])];
-         };
-      })
-    ];
-  pkgs = import <nixpkgs> { inherit overlays; };
-in
-  { gobanme-no-yagai-purojekuto = pkgs.haskellPackages.gobanme-no-yagai-purojekuto;
-  }
diff --git a/fixtures/gobanme-no-yagai-purojekuto/gobanme-no-yagai-purojekuto.cabal b/fixtures/gobanme-no-yagai-purojekuto/gobanme-no-yagai-purojekuto.cabal
deleted file mode 100644
index 86fb3bc..0000000
--- a/fixtures/gobanme-no-yagai-purojekuto/gobanme-no-yagai-purojekuto.cabal
+++ /dev/null
@@ -1,11 +0,0 @@
-name: gobanme-no-yagai-purojekuto
-version: 1.0.0
-license: BSD3
-license-file: LICENSE
-cabal-version: >= 1.18
-build-type: Simple
-
-executable gobanme-no-yagai-purojekuto
-    build-depends: base < 5, foldl, text, turtle
-    main-is: Main.hs
-    default-language: Haskell2010
diff --git a/fixtures/gobanme-no-yagai-purojekuto/setup_test.sh b/fixtures/gobanme-no-yagai-purojekuto/setup_test.sh
deleted file mode 100755
index 9a4f0e4..0000000
--- a/fixtures/gobanme-no-yagai-purojekuto/setup_test.sh
+++ /dev/null
@@ -1,13 +0,0 @@
-#!/bin/bash
-set -euo pipefail
-
-setup_test() {
-    local this_dir=$(dirname "${BASH_SOURCE[${#BASH_SOURCE[@]} - 1]}")
-    pushd $this_dir > /dev/null
-
-    $HOZ_TEST_CMD fetch --subpath subdir-root/a-subdir https://github.com/adetokunbo/example-fetched-haskell-overridez
-
-    popd > /dev/null
-}
-
-setup_test
diff --git a/fixtures/hachibanme-no-purojekuto/.gitignore b/fixtures/hachibanme-no-purojekuto/.gitignore
deleted file mode 100644
index 81259c4..0000000
--- a/fixtures/hachibanme-no-purojekuto/.gitignore
+++ /dev/null
@@ -1 +0,0 @@
-nix
diff --git a/fixtures/hachibanme-no-purojekuto/DESC b/fixtures/hachibanme-no-purojekuto/DESC
deleted file mode 100644
index 09cd83a..0000000
--- a/fixtures/hachibanme-no-purojekuto/DESC
+++ /dev/null
@@ -1 +0,0 @@
-create an overlay from nix-exprs created by cabal2nix with github https uris saved in a specific directory
diff --git a/fixtures/hachibanme-no-purojekuto/Main.hs b/fixtures/hachibanme-no-purojekuto/Main.hs
deleted file mode 100644
index e335da6..0000000
--- a/fixtures/hachibanme-no-purojekuto/Main.hs
+++ /dev/null
@@ -1,8 +0,0 @@
-{-# LANGUAGE OverloadedStrings #-}
-
-module Main where
-
-import Turtle
-
-main :: IO ()
-main = echo "Hello, world!"
diff --git a/fixtures/hachibanme-no-purojekuto/hachibanme-no-purojekuto.cabal b/fixtures/hachibanme-no-purojekuto/hachibanme-no-purojekuto.cabal
deleted file mode 100644
index 2c23845..0000000
--- a/fixtures/hachibanme-no-purojekuto/hachibanme-no-purojekuto.cabal
+++ /dev/null
@@ -1,11 +0,0 @@
-name: hachibanme-no-purojekuto
-version: 1.0.0
-license: BSD3
-license-file: LICENSE
-cabal-version: >= 1.18
-build-type: Simple
-
-executable hachibanme-no-purojekuto
-    build-depends: base < 5, foldl, text, turtle
-    main-is: Main.hs
-    default-language: Haskell2010
diff --git a/fixtures/hachibanme-no-purojekuto/setup_test.sh b/fixtures/hachibanme-no-purojekuto/setup_test.sh
deleted file mode 100755
index f4939d5..0000000
--- a/fixtures/hachibanme-no-purojekuto/setup_test.sh
+++ /dev/null
@@ -1,31 +0,0 @@
-#!/bin/bash
-set -euo pipefail
-
-setup_test() {
-    local this_dir=$(dirname "${BASH_SOURCE[${#BASH_SOURCE[@]} - 1]}")
-    pushd $this_dir > /dev/null
-    local cwd=$(pwd)
-    local test_name="${cwd##*/}"
-
-    # Make a directory under the tmp root in which to save the output
-    local dst_dir="${HOZ_TMP_DIR}/dst/${test_name}"
-    mkdir -p $dst_dir
-
-    # Set up the configuration
-    $HOZ_TEST_CMD --flag-override DontCheck -o $dst_dir https://github.com/pcapriotti/optparse-applicative
-    $HOZ_TEST_CMD --flag-override DoJailbreak -o $dst_dir https://github.com/Gabriel439/Haskell-Turtle-Library
-    $HOZ_TEST_CMD --flag-override DoJailbreak -o $dst_dir https://github.com/Gabriel439/Haskell-Foldl-Library
-    $HOZ_TEST_CMD --flag-override DoJailbreak -o $dst_dir https://github.com/Gabriel439/Haskell-Managed-Library
-
-    (cat <<EOF
-let
-  overridez = import ./haskell-overridez.nix;
-in
-  overridez.allIn ${dst_dir}/nix
-EOF
-    ) > ./nix/indirect_import.nix
-
-    popd > /dev/null
-}
-
-setup_test
diff --git a/fixtures/ichibanme-no-yagai-purojekuto/.gitignore b/fixtures/ichibanme-no-yagai-purojekuto/.gitignore
deleted file mode 100644
index 81259c4..0000000
--- a/fixtures/ichibanme-no-yagai-purojekuto/.gitignore
+++ /dev/null
@@ -1 +0,0 @@
-nix
diff --git a/fixtures/ichibanme-no-yagai-purojekuto/DESC b/fixtures/ichibanme-no-yagai-purojekuto/DESC
deleted file mode 100644
index 2f9a765..0000000
--- a/fixtures/ichibanme-no-yagai-purojekuto/DESC
+++ /dev/null
@@ -1 +0,0 @@
-create an overlay from config fetched from a github repository
diff --git a/fixtures/ichibanme-no-yagai-purojekuto/LICENSE b/fixtures/ichibanme-no-yagai-purojekuto/LICENSE
deleted file mode 100644
index f1036a4..0000000
--- a/fixtures/ichibanme-no-yagai-purojekuto/LICENSE
+++ /dev/null
@@ -1,11 +0,0 @@
-Copyright (c) 2018, Timothy Emiola
-
-Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:
-
-1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
-
-2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.
-
-3. Neither the name of the copyright holder nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.
-
-THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
diff --git a/fixtures/ichibanme-no-yagai-purojekuto/Main.hs b/fixtures/ichibanme-no-yagai-purojekuto/Main.hs
deleted file mode 100644
index e335da6..0000000
--- a/fixtures/ichibanme-no-yagai-purojekuto/Main.hs
+++ /dev/null
@@ -1,8 +0,0 @@
-{-# LANGUAGE OverloadedStrings #-}
-
-module Main where
-
-import Turtle
-
-main :: IO ()
-main = echo "Hello, world!"
diff --git a/fixtures/ichibanme-no-yagai-purojekuto/default.nix b/fixtures/ichibanme-no-yagai-purojekuto/default.nix
deleted file mode 100644
index f51147d..0000000
--- a/fixtures/ichibanme-no-yagai-purojekuto/default.nix
+++ /dev/null
@@ -1,26 +0,0 @@
-let
-  overridez = import ./nix/haskell-overridez.nix;
-  githubKara = overridez.allIn ./nix/github.com/adetokunbo/example-fetched-haskell-overridez;
-  overlays =
-    let dropTestPkgs = haskellPackagesNew: haskellPackagesOld: {
-            foldl = null;
-            managed = null;
-            optparse-applicative = null;
-            turtle = null;
-            ichibanme-no-yagai-purojekuto = haskellPackagesNew.callPackage ./nix/ichibanme-no-yagai-purojekuto.nix {};
-          };
-    in [
-      (newPkgs: oldPkgs:
-         let
-           inherit (oldPkgs.lib) composeExtensions fold;
-           composeExtensionsList = fold composeExtensions (_: _: {});
-         in {
-           haskellPackages = oldPkgs.haskellPackages.override {
-             overrides = composeExtensionsList [dropTestPkgs (overridez.combineAllIn ./nix [githubKara])];
-         };
-      })
-    ];
-  pkgs = import <nixpkgs> { inherit overlays; };
-in
-  { ichibanme-no-yagai-purojekuto = pkgs.haskellPackages.ichibanme-no-yagai-purojekuto;
-  }
diff --git a/fixtures/ichibanme-no-yagai-purojekuto/ichibanme-no-yagai-purojekuto.cabal b/fixtures/ichibanme-no-yagai-purojekuto/ichibanme-no-yagai-purojekuto.cabal
deleted file mode 100644
index b6cc8e8..0000000
--- a/fixtures/ichibanme-no-yagai-purojekuto/ichibanme-no-yagai-purojekuto.cabal
+++ /dev/null
@@ -1,11 +0,0 @@
-name: ichibanme-no-yagai-purojekuto
-version: 1.0.0
-license: BSD3
-license-file: LICENSE
-cabal-version: >= 1.18
-build-type: Simple
-
-executable ichibanme-no-yagai-purojekuto
-    build-depends: base < 5, foldl, text, turtle
-    main-is: Main.hs
-    default-language: Haskell2010
diff --git a/fixtures/ichibanme-no-yagai-purojekuto/setup_test.sh b/fixtures/ichibanme-no-yagai-purojekuto/setup_test.sh
deleted file mode 100755
index 42fec57..0000000
--- a/fixtures/ichibanme-no-yagai-purojekuto/setup_test.sh
+++ /dev/null
@@ -1,13 +0,0 @@
-#!/bin/bash
-set -euo pipefail
-
-setup_test() {
-    local this_dir=$(dirname "${BASH_SOURCE[${#BASH_SOURCE[@]} - 1]}")
-    pushd $this_dir > /dev/null
-
-    $HOZ_TEST_CMD fetch https://github.com/adetokunbo/example-fetched-haskell-overridez
-
-    popd > /dev/null
-}
-
-setup_test
diff --git a/fixtures/kyuubanme-no-purojekuto/.gitignore b/fixtures/kyuubanme-no-purojekuto/.gitignore
deleted file mode 100644
index 81259c4..0000000
--- a/fixtures/kyuubanme-no-purojekuto/.gitignore
+++ /dev/null
@@ -1 +0,0 @@
-nix
diff --git a/fixtures/kyuubanme-no-purojekuto/DESC b/fixtures/kyuubanme-no-purojekuto/DESC
deleted file mode 100644
index bd7ac54..0000000
--- a/fixtures/kyuubanme-no-purojekuto/DESC
+++ /dev/null
@@ -1 +0,0 @@
-create an overlay from nix-exprs created by cabal2nix on a subdirectory of a github https repository
diff --git a/fixtures/kyuubanme-no-purojekuto/LICENSE b/fixtures/kyuubanme-no-purojekuto/LICENSE
deleted file mode 100644
index f1036a4..0000000
--- a/fixtures/kyuubanme-no-purojekuto/LICENSE
+++ /dev/null
@@ -1,11 +0,0 @@
-Copyright (c) 2018, Timothy Emiola
-
-Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:
-
-1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
-
-2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.
-
-3. Neither the name of the copyright holder nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.
-
-THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
diff --git a/fixtures/kyuubanme-no-purojekuto/Main.hs b/fixtures/kyuubanme-no-purojekuto/Main.hs
deleted file mode 100644
index 9efa0f2..0000000
--- a/fixtures/kyuubanme-no-purojekuto/Main.hs
+++ /dev/null
@@ -1,22 +0,0 @@
-{-# LANGUAGE FlexibleContexts           #-}
-{-# LANGUAGE FlexibleInstances          #-}
-{-# LANGUAGE MultiParamTypeClasses      #-}
-{-# LANGUAGE OverloadedStrings          #-}
-{-# LANGUAGE StandaloneDeriving         #-}
-
-module Main where
-
-import           Control.Monad.Log
-import           Data.Text.Prettyprint.Doc (Doc)
-import           System.IO (stdout)
-
-main :: IO ()
-main =
-  withFDHandler defaultBatchingOptions stdout 0.4 80 $ \logToStdout ->
-  runLoggingT testApp (logToStdout . renderWithSeverity id)
-
-
-testApp :: MonadLog (WithSeverity (Doc ann)) m => m ()
-testApp = do
-  logMessage (WithSeverity Informational "Don't mind me")
-  logMessage (WithSeverity Error "But do mind me!")
diff --git a/fixtures/kyuubanme-no-purojekuto/setup_test.sh b/fixtures/kyuubanme-no-purojekuto/setup_test.sh
deleted file mode 100755
index e99580a..0000000
--- a/fixtures/kyuubanme-no-purojekuto/setup_test.sh
+++ /dev/null
@@ -1,13 +0,0 @@
-#!/bin/bash
-set -euo pipefail
-
-setup_test() {
-    local this_dir=$(dirname "${BASH_SOURCE[${#BASH_SOURCE[@]} - 1]}")
-    pushd $this_dir > /dev/null
-
-    $HOZ_TEST_CMD https://github.com/jship/logging-effect-extra -- --subpath logging-effect-extra-file
-
-    popd > /dev/null
-}
-
-setup_test
diff --git a/fixtures/nanabanme-no-purojekuto/.gitignore b/fixtures/nanabanme-no-purojekuto/.gitignore
deleted file mode 100644
index 81259c4..0000000
--- a/fixtures/nanabanme-no-purojekuto/.gitignore
+++ /dev/null
@@ -1 +0,0 @@
-nix
diff --git a/fixtures/nanabanme-no-purojekuto/DESC b/fixtures/nanabanme-no-purojekuto/DESC
deleted file mode 100644
index ca7ee0b..0000000
--- a/fixtures/nanabanme-no-purojekuto/DESC
+++ /dev/null
@@ -1 +0,0 @@
-cannot create an overlay when dependencies are removed as a control
diff --git a/fixtures/nanabanme-no-purojekuto/LICENSE b/fixtures/nanabanme-no-purojekuto/LICENSE
deleted file mode 100644
index f1036a4..0000000
--- a/fixtures/nanabanme-no-purojekuto/LICENSE
+++ /dev/null
@@ -1,11 +0,0 @@
-Copyright (c) 2018, Timothy Emiola
-
-Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:
-
-1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
-
-2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.
-
-3. Neither the name of the copyright holder nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.
-
-THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
diff --git a/fixtures/nanabanme-no-purojekuto/Main.hs b/fixtures/nanabanme-no-purojekuto/Main.hs
deleted file mode 100644
index e335da6..0000000
--- a/fixtures/nanabanme-no-purojekuto/Main.hs
+++ /dev/null
@@ -1,8 +0,0 @@
-{-# LANGUAGE OverloadedStrings #-}
-
-module Main where
-
-import Turtle
-
-main :: IO ()
-main = echo "Hello, world!"
diff --git a/fixtures/nanabanme-no-purojekuto/nanabanme-no-purojekuto.cabal b/fixtures/nanabanme-no-purojekuto/nanabanme-no-purojekuto.cabal
deleted file mode 100644
index e51ce0b..0000000
--- a/fixtures/nanabanme-no-purojekuto/nanabanme-no-purojekuto.cabal
+++ /dev/null
@@ -1,11 +0,0 @@
-name: nanabanme-no-purojekuto
-version: 1.0.0
-license: BSD3
-license-file: LICENSE
-cabal-version: >= 1.18
-build-type: Simple
-
-executable nanabanme-no-purojekuto
-    build-depends: base < 5, foldl, text, turtle
-    main-is: Main.hs
-    default-language: Haskell2010
diff --git a/fixtures/nanabanme-no-purojekuto/setup_test.sh b/fixtures/nanabanme-no-purojekuto/setup_test.sh
deleted file mode 100755
index eb5ccf2..0000000
--- a/fixtures/nanabanme-no-purojekuto/setup_test.sh
+++ /dev/null
@@ -1,16 +0,0 @@
-#!/bin/bash
-set -euo pipefail
-
-setup_test() {
-    local this_dir=$(dirname "${BASH_SOURCE[${#BASH_SOURCE[@]} - 1]}")
-    pushd $this_dir > /dev/null
-
-    $HOZ_TEST_CMD --flag-override DontCheck cabal://optparse-applicative-0.14.2.0
-    $HOZ_TEST_CMD --flag-override DoJailbreak cabal://turtle-1.5.12
-    $HOZ_TEST_CMD --flag-override DoJailbreak cabal://foldl-1.4.5
-    $HOZ_TEST_CMD --flag-override DoJailbreak cabal://managed-1.0.6
-
-    popd > /dev/null
-}
-
-setup_test
diff --git a/fixtures/nanabanme-no-purojekuto/test.sh b/fixtures/nanabanme-no-purojekuto/test.sh
deleted file mode 100644
index 4922603..0000000
--- a/fixtures/nanabanme-no-purojekuto/test.sh
+++ /dev/null
@@ -1,12 +0,0 @@
-#!/bin/bash
-
-test() {
-    nix-build --no-out-link || return 0
-    test_desc="$(cat DESC)"
-    echo
-    echo "FAILED: '$test_desc' in $(pwd)"
-    echo
-    return 1
-}
-
-test
diff --git a/fixtures/nibanme-no-yagai-purojekuto/DESC b/fixtures/nibanme-no-yagai-purojekuto/DESC
deleted file mode 100644
index d1bbccd..0000000
--- a/fixtures/nibanme-no-yagai-purojekuto/DESC
+++ /dev/null
@@ -1 +0,0 @@
-cannot fetch config files from an invalid repository
diff --git a/fixtures/nibanme-no-yagai-purojekuto/nibanme-no-yagi-purojekuto.cabal b/fixtures/nibanme-no-yagai-purojekuto/nibanme-no-yagi-purojekuto.cabal
deleted file mode 100644
index 3d2c29d..0000000
--- a/fixtures/nibanme-no-yagai-purojekuto/nibanme-no-yagi-purojekuto.cabal
+++ /dev/null
@@ -1,11 +0,0 @@
-name: nibanme-no-yagai-purojekuto
-version: 1.0.0
-license: BSD3
-license-file: LICENSE
-cabal-version: >= 1.18
-build-type: Simple
-
-executable nibanme-no-yagai-purojekuto
-    build-depends: base < 5, foldl, text, turtle
-    main-is: Main.hs
-    default-language: Haskell2010
diff --git a/fixtures/nibanme-no-yagai-purojekuto/setup_test.sh b/fixtures/nibanme-no-yagai-purojekuto/setup_test.sh
deleted file mode 100755
index 9588f56..0000000
--- a/fixtures/nibanme-no-yagai-purojekuto/setup_test.sh
+++ /dev/null
@@ -1,8 +0,0 @@
-#!/bin/bash
-set -euo pipefail
-
-setup_test() {
-    echo "skipped setup"
-}
-
-setup_test
diff --git a/fixtures/nibanme-no-yagai-purojekuto/test.sh b/fixtures/nibanme-no-yagai-purojekuto/test.sh
deleted file mode 100755
index 66fe451..0000000
--- a/fixtures/nibanme-no-yagai-purojekuto/test.sh
+++ /dev/null
@@ -1,13 +0,0 @@
-#!/bin/bash
-
-test() {
-    local invalid_fetch=https://github.com/adetokunbo/automine
-    $HOZ_TEST_CMD fetch $invalid_fetch || return 0
-    test_desc="$(cat DESC)"
-    echo
-    echo "FAILED: '$test_desc'"
-    echo
-    return 1
-}
-
-test
diff --git a/fixtures/rokubanme-no-purojekuto/.gitignore b/fixtures/rokubanme-no-purojekuto/.gitignore
deleted file mode 100644
index 81259c4..0000000
--- a/fixtures/rokubanme-no-purojekuto/.gitignore
+++ /dev/null
@@ -1 +0,0 @@
-nix
diff --git a/fixtures/rokubanme-no-purojekuto/DESC b/fixtures/rokubanme-no-purojekuto/DESC
deleted file mode 100644
index 8a1f29d..0000000
--- a/fixtures/rokubanme-no-purojekuto/DESC
+++ /dev/null
@@ -1 +0,0 @@
-create an overlay from git json created by nix-prefetch-git
diff --git a/fixtures/rokubanme-no-purojekuto/LICENSE b/fixtures/rokubanme-no-purojekuto/LICENSE
deleted file mode 100644
index f1036a4..0000000
--- a/fixtures/rokubanme-no-purojekuto/LICENSE
+++ /dev/null
@@ -1,11 +0,0 @@
-Copyright (c) 2018, Timothy Emiola
-
-Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:
-
-1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
-
-2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.
-
-3. Neither the name of the copyright holder nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.
-
-THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
diff --git a/fixtures/rokubanme-no-purojekuto/Main.hs b/fixtures/rokubanme-no-purojekuto/Main.hs
deleted file mode 100644
index e335da6..0000000
--- a/fixtures/rokubanme-no-purojekuto/Main.hs
+++ /dev/null
@@ -1,8 +0,0 @@
-{-# LANGUAGE OverloadedStrings #-}
-
-module Main where
-
-import Turtle
-
-main :: IO ()
-main = echo "Hello, world!"
diff --git a/fixtures/rokubanme-no-purojekuto/default.nix b/fixtures/rokubanme-no-purojekuto/default.nix
deleted file mode 100644
index a4e9d37..0000000
--- a/fixtures/rokubanme-no-purojekuto/default.nix
+++ /dev/null
@@ -1,25 +0,0 @@
-let
-  overridez = import ./nix/haskell-overridez.nix;
-  overlays =
-    let dropTestPkgs = haskellPackagesNew: haskellPackagesOld: {
-            foldl = null;
-            managed = null;
-            optparse-applicative = null;
-            turtle = null;
-            rokubanme-no-purojekuto = haskellPackagesNew.callPackage ./nix/rokubanme-no-purojekuto.nix {};
-          };
-    in [
-      (newPkgs: oldPkgs:
-         let
-           inherit (oldPkgs.lib) composeExtensions fold;
-           composeExtensionsList = fold composeExtensions (_: _: {});
-         in {
-           haskellPackages = oldPkgs.haskellPackages.override {
-             overrides = composeExtensionsList [dropTestPkgs (overridez.allIn ./nix)];
-         };
-      })
-    ];
-  pkgs = import <nixpkgs> { inherit overlays; };
-in
-  { rokubanme-no-purojekuto = pkgs.haskellPackages.rokubanme-no-purojekuto;
-  }
diff --git a/fixtures/rokubanme-no-purojekuto/rokubanme-no-purojekuto.cabal b/fixtures/rokubanme-no-purojekuto/rokubanme-no-purojekuto.cabal
deleted file mode 100644
index 59fc516..0000000
--- a/fixtures/rokubanme-no-purojekuto/rokubanme-no-purojekuto.cabal
+++ /dev/null
@@ -1,11 +0,0 @@
-name: rokubanme-no-purojekuto
-version: 1.0.0
-license: BSD3
-license-file: LICENSE
-cabal-version: >= 1.18
-build-type: Simple
-
-executable rokubanme-no-purojekuto
-    build-depends: base < 5, foldl, text, turtle
-    main-is: Main.hs
-    default-language: Haskell2010
diff --git a/fixtures/rokubanme-no-purojekuto/setup_test.sh b/fixtures/rokubanme-no-purojekuto/setup_test.sh
deleted file mode 100755
index ebff6d7..0000000
--- a/fixtures/rokubanme-no-purojekuto/setup_test.sh
+++ /dev/null
@@ -1,19 +0,0 @@
-#!/bin/bash
-set -euo pipefail
-
-setup_test() {
-    local this_dir=$(dirname "${BASH_SOURCE[${#BASH_SOURCE[@]} - 1]}")
-    pushd $this_dir > /dev/null
-
-    # Using -g with foldl or optparse-applicative makes cabal2nix infinitely
-    # recurse when converting the json to nix-expr
-    $HOZ_TEST_CMD --flag-override DontCheck https://github.com/pcapriotti/optparse-applicative
-    $HOZ_TEST_CMD --flag-override DontCheck https://github.com/Gabriel439/Haskell-Foldl-Library
-
-    $HOZ_TEST_CMD --flag-override DoJailbreak -g Gabriel439/Haskell-Turtle-Library
-    $HOZ_TEST_CMD --flag-override DoJailbreak -g Gabriel439/Haskell-Managed-Library
-
-    popd > /dev/null
-}
-
-setup_test
diff --git a/fixtures/sanbanme-no-yagai-purojekuto/.gitignore b/fixtures/sanbanme-no-yagai-purojekuto/.gitignore
deleted file mode 100644
index 81259c4..0000000
--- a/fixtures/sanbanme-no-yagai-purojekuto/.gitignore
+++ /dev/null
@@ -1 +0,0 @@
-nix
diff --git a/fixtures/sanbanme-no-yagai-purojekuto/DESC b/fixtures/sanbanme-no-yagai-purojekuto/DESC
deleted file mode 100644
index 78ce7ad..0000000
--- a/fixtures/sanbanme-no-yagai-purojekuto/DESC
+++ /dev/null
@@ -1 +0,0 @@
-create an overlay from config fetched from a local git repository
diff --git a/fixtures/sanbanme-no-yagai-purojekuto/LICENSE b/fixtures/sanbanme-no-yagai-purojekuto/LICENSE
deleted file mode 100644
index f1036a4..0000000
--- a/fixtures/sanbanme-no-yagai-purojekuto/LICENSE
+++ /dev/null
@@ -1,11 +0,0 @@
-Copyright (c) 2018, Timothy Emiola
-
-Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:
-
-1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
-
-2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.
-
-3. Neither the name of the copyright holder nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.
-
-THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
diff --git a/fixtures/sanbanme-no-yagai-purojekuto/Main.hs b/fixtures/sanbanme-no-yagai-purojekuto/Main.hs
deleted file mode 100644
index e335da6..0000000
--- a/fixtures/sanbanme-no-yagai-purojekuto/Main.hs
+++ /dev/null
@@ -1,8 +0,0 @@
-{-# LANGUAGE OverloadedStrings #-}
-
-module Main where
-
-import Turtle
-
-main :: IO ()
-main = echo "Hello, world!"
diff --git a/fixtures/sanbanme-no-yagai-purojekuto/default.nix b/fixtures/sanbanme-no-yagai-purojekuto/default.nix
deleted file mode 100644
index 6c21a5c..0000000
--- a/fixtures/sanbanme-no-yagai-purojekuto/default.nix
+++ /dev/null
@@ -1,26 +0,0 @@
-let
-  overridez = import ./nix/haskell-overridez.nix;
-  localhostKara = overridez.allIn ./nix/localhost/sanbanme-no-yagai-purojekuto;
-  overlays =
-    let dropTestPkgs = haskellPackagesNew: haskellPackagesOld: {
-            foldl = null;
-            managed = null;
-            optparse-applicative = null;
-            turtle = null;
-            sanbanme-no-yagai-purojekuto = haskellPackagesNew.callPackage ./nix/sanbanme-no-yagai-purojekuto.nix {};
-          };
-    in [
-      (newPkgs: oldPkgs:
-         let
-           inherit (oldPkgs.lib) composeExtensions fold;
-           composeExtensionsList = fold composeExtensions (_: _: {});
-         in {
-           haskellPackages = oldPkgs.haskellPackages.override {
-             overrides = composeExtensionsList [dropTestPkgs (overridez.combineAllIn ./nix [localhostKara])];
-         };
-      })
-    ];
-  pkgs = import <nixpkgs> { inherit overlays; };
-in
-  { sanbanme-no-yagai-purojekuto = pkgs.haskellPackages.sanbanme-no-yagai-purojekuto;
-  }
diff --git a/fixtures/sanbanme-no-yagai-purojekuto/sanbanme-no-yagai-purojekuto.cabal b/fixtures/sanbanme-no-yagai-purojekuto/sanbanme-no-yagai-purojekuto.cabal
deleted file mode 100644
index 4e03d3c..0000000
--- a/fixtures/sanbanme-no-yagai-purojekuto/sanbanme-no-yagai-purojekuto.cabal
+++ /dev/null
@@ -1,11 +0,0 @@
-name: sanbanme-no-yagai-purojekuto
-version: 1.0.0
-license: BSD3
-license-file: LICENSE
-cabal-version: >= 1.18
-build-type: Simple
-
-executable sanbanme-no-yagai-purojekuto
-    build-depends: base < 5, foldl, text, turtle
-    main-is: Main.hs
-    default-language: Haskell2010
diff --git a/fixtures/sanbanme-no-yagai-purojekuto/setup_test.sh b/fixtures/sanbanme-no-yagai-purojekuto/setup_test.sh
deleted file mode 100755
index 5ad6003..0000000
--- a/fixtures/sanbanme-no-yagai-purojekuto/setup_test.sh
+++ /dev/null
@@ -1,25 +0,0 @@
-#!/bin/bash
-set -euo pipefail
-setup_test() {
-    local this_dir=$(dirname "${BASH_SOURCE[${#BASH_SOURCE[@]} - 1]}")
-    pushd $this_dir > /dev/null
-    local cwd=$(pwd)
-    local out_dir="${HOZ_TMP_DIR}/${cwd##*/}"
-     mkdir -p $out_dir
-
-    # fetch a recent version of the github example, save it locally, and use
-    # that as a local git repo (needs all the flags belows; plus the revision and hash)
-    nix-prefetch-git --quiet \
-                     --out $out_dir \
-                     --builder \
-                     --leave-dotGit \
-                     https://github.com/adetokunbo/example-fetched-haskell-overridez \
-                     e1dc13ae7dcb3a4c4b7f426a94ecf523532ea574 \
-                     0sapkc9mpk95dlq6n87z8xa8w4r0cnxxpnyp971m5phjpbn83c7q
-    ls -l $out_dir
-
-    $HOZ_TEST_CMD fetch "file://${out_dir}"
-    popd > /dev/null
-}
-
-setup_test
diff --git a/fixtures/yonbanme-no-purojekuto/.gitignore b/fixtures/yonbanme-no-purojekuto/.gitignore
deleted file mode 100644
index 81259c4..0000000
--- a/fixtures/yonbanme-no-purojekuto/.gitignore
+++ /dev/null
@@ -1 +0,0 @@
-nix
diff --git a/fixtures/yonbanme-no-purojekuto/DESC b/fixtures/yonbanme-no-purojekuto/DESC
deleted file mode 100644
index a9a3966..0000000
--- a/fixtures/yonbanme-no-purojekuto/DESC
+++ /dev/null
@@ -1 +0,0 @@
-create an overlay from nix-exprs created by cabal2nix with cabal:// uris
diff --git a/fixtures/yonbanme-no-purojekuto/LICENSE b/fixtures/yonbanme-no-purojekuto/LICENSE
deleted file mode 100644
index f1036a4..0000000
--- a/fixtures/yonbanme-no-purojekuto/LICENSE
+++ /dev/null
@@ -1,11 +0,0 @@
-Copyright (c) 2018, Timothy Emiola
-
-Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:
-
-1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
-
-2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.
-
-3. Neither the name of the copyright holder nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.
-
-THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
diff --git a/fixtures/yonbanme-no-purojekuto/Main.hs b/fixtures/yonbanme-no-purojekuto/Main.hs
deleted file mode 100644
index e335da6..0000000
--- a/fixtures/yonbanme-no-purojekuto/Main.hs
+++ /dev/null
@@ -1,8 +0,0 @@
-{-# LANGUAGE OverloadedStrings #-}
-
-module Main where
-
-import Turtle
-
-main :: IO ()
-main = echo "Hello, world!"
diff --git a/fixtures/yonbanme-no-purojekuto/default.nix b/fixtures/yonbanme-no-purojekuto/default.nix
deleted file mode 100644
index c675692..0000000
--- a/fixtures/yonbanme-no-purojekuto/default.nix
+++ /dev/null
@@ -1,25 +0,0 @@
-let
-  overridez = import ./nix/haskell-overridez.nix;
-  overlays =
-    let dropTestPkgs = haskellPackagesNew: haskellPackagesOld: {
-            foldl = null;
-            managed = null;
-            optparse-applicative = null;
-            turtle = null;
-            yonbanme-no-purojekuto = haskellPackagesNew.callPackage ./nix/yonbanme-no-purojekuto.nix {};
-          };
-    in [
-      (newPkgs: oldPkgs:
-         let
-           inherit (oldPkgs.lib) composeExtensions fold;
-           composeExtensionsList = fold composeExtensions (_: _: {});
-         in {
-           haskellPackages = oldPkgs.haskellPackages.override {
-             overrides = composeExtensionsList [dropTestPkgs (overridez.allIn ./nix)];
-         };
-      })
-    ];
-  pkgs = import <nixpkgs> { inherit overlays; };
-in
-  { yonbanme-no-purojekuto = pkgs.haskellPackages.yonbanme-no-purojekuto;
-  }
diff --git a/fixtures/yonbanme-no-purojekuto/setup_test.sh b/fixtures/yonbanme-no-purojekuto/setup_test.sh
deleted file mode 100755
index eb5ccf2..0000000
--- a/fixtures/yonbanme-no-purojekuto/setup_test.sh
+++ /dev/null
@@ -1,16 +0,0 @@
-#!/bin/bash
-set -euo pipefail
-
-setup_test() {
-    local this_dir=$(dirname "${BASH_SOURCE[${#BASH_SOURCE[@]} - 1]}")
-    pushd $this_dir > /dev/null
-
-    $HOZ_TEST_CMD --flag-override DontCheck cabal://optparse-applicative-0.14.2.0
-    $HOZ_TEST_CMD --flag-override DoJailbreak cabal://turtle-1.5.12
-    $HOZ_TEST_CMD --flag-override DoJailbreak cabal://foldl-1.4.5
-    $HOZ_TEST_CMD --flag-override DoJailbreak cabal://managed-1.0.6
-
-    popd > /dev/null
-}
-
-setup_test
diff --git a/fixtures/yonbanme-no-purojekuto/yonbanme-no-purojekuto.cabal b/fixtures/yonbanme-no-purojekuto/yonbanme-no-purojekuto.cabal
deleted file mode 100644
index 5f53ab7..0000000
--- a/fixtures/yonbanme-no-purojekuto/yonbanme-no-purojekuto.cabal
+++ /dev/null
@@ -1,11 +0,0 @@
-name: yonbanme-no-purojekuto
-version: 1.0.0
-license: BSD3
-license-file: LICENSE
-cabal-version: >= 1.18
-build-type: Simple
-
-executable yonbanme-no-purojekuto
-    build-depends: base < 5, foldl, text, turtle
-    main-is: Main.hs
-    default-language: Haskell2010
diff --git a/fixtures/yonbanme-no-yagai-purojekuto/.gitignore b/fixtures/yonbanme-no-yagai-purojekuto/.gitignore
deleted file mode 100644
index 81259c4..0000000
--- a/fixtures/yonbanme-no-yagai-purojekuto/.gitignore
+++ /dev/null
@@ -1 +0,0 @@
-nix
diff --git a/fixtures/yonbanme-no-yagai-purojekuto/DESC b/fixtures/yonbanme-no-yagai-purojekuto/DESC
deleted file mode 100644
index 5de79a4..0000000
--- a/fixtures/yonbanme-no-yagai-purojekuto/DESC
+++ /dev/null
@@ -1 +0,0 @@
-create an overlay from config fetched from a local git repository in a specific directory
diff --git a/fixtures/yonbanme-no-yagai-purojekuto/LICENSE b/fixtures/yonbanme-no-yagai-purojekuto/LICENSE
deleted file mode 100644
index f1036a4..0000000
--- a/fixtures/yonbanme-no-yagai-purojekuto/LICENSE
+++ /dev/null
@@ -1,11 +0,0 @@
-Copyright (c) 2018, Timothy Emiola
-
-Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:
-
-1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
-
-2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.
-
-3. Neither the name of the copyright holder nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.
-
-THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
diff --git a/fixtures/yonbanme-no-yagai-purojekuto/Main.hs b/fixtures/yonbanme-no-yagai-purojekuto/Main.hs
deleted file mode 100644
index e335da6..0000000
--- a/fixtures/yonbanme-no-yagai-purojekuto/Main.hs
+++ /dev/null
@@ -1,8 +0,0 @@
-{-# LANGUAGE OverloadedStrings #-}
-
-module Main where
-
-import Turtle
-
-main :: IO ()
-main = echo "Hello, world!"
diff --git a/fixtures/yonbanme-no-yagai-purojekuto/default.nix b/fixtures/yonbanme-no-yagai-purojekuto/default.nix
deleted file mode 100644
index 52947a5..0000000
--- a/fixtures/yonbanme-no-yagai-purojekuto/default.nix
+++ /dev/null
@@ -1,26 +0,0 @@
-let
-  overridez = import ./nix/haskell-overridez.nix;
-  localhostKara = import ./nix/indirect_import.nix;
-  overlays =
-    let dropTestPkgs = haskellPackagesNew: haskellPackagesOld: {
-            foldl = null;
-            managed = null;
-            optparse-applicative = null;
-            turtle = null;
-            yonbanme-no-yagai-purojekuto = haskellPackagesNew.callPackage ./nix/yonbanme-no-yagai-purojekuto.nix {};
-          };
-    in [
-      (newPkgs: oldPkgs:
-         let
-           inherit (oldPkgs.lib) composeExtensions fold;
-           composeExtensionsList = fold composeExtensions (_: _: {});
-         in {
-           haskellPackages = oldPkgs.haskellPackages.override {
-             overrides = composeExtensionsList [dropTestPkgs (overridez.combineAllIn ./nix [localhostKara])];
-         };
-      })
-    ];
-  pkgs = import <nixpkgs> { inherit overlays; };
-in
-  { yonbanme-no-yagai-purojekuto = pkgs.haskellPackages.yonbanme-no-yagai-purojekuto;
-  }
diff --git a/fixtures/yonbanme-no-yagai-purojekuto/setup_test.sh b/fixtures/yonbanme-no-yagai-purojekuto/setup_test.sh
deleted file mode 100755
index 705cbb6..0000000
--- a/fixtures/yonbanme-no-yagai-purojekuto/setup_test.sh
+++ /dev/null
@@ -1,38 +0,0 @@
-#!/bin/bash
-set -euo pipefail
-
-setup_test() {
-    local this_dir=$(dirname "${BASH_SOURCE[${#BASH_SOURCE[@]} - 1]}")
-    pushd $this_dir > /dev/null
-    local cwd=$(pwd)
-    local test_name="${cwd##*/}"
-    local out_dir="${HOZ_TMP_DIR}/${test_name}"
-    mkdir -p $out_dir
-
-    # fetch the recent version of the github example, save it locally, and use
-    # that as a local git repo (needs all the flags belows; plus the revision and hash)
-    nix-prefetch-git --quiet \
-                     --out $out_dir \
-                     --builder \
-                     --leave-dotGit \
-                     https://github.com/adetokunbo/example-fetched-haskell-overridez \
-                     e1dc13ae7dcb3a4c4b7f426a94ecf523532ea574 \
-                     0sapkc9mpk95dlq6n87z8xa8w4r0cnxxpnyp971m5phjpbn83c7q
-    ls -l $out_dir
-
-    # Make a directory under the tmp root in which to save the output
-    local dst_dir="${HOZ_TMP_DIR}/dst/${test_name}"
-    mkdir -p $dst_dir
-    (cat <<EOF
-let
-  overridez = import ./haskell-overridez.nix;
-in
-  overridez.allIn ${dst_dir}/nix/localhost/${test_name}
-EOF
-    ) > ./nix/indirect_import.nix
-    $HOZ_TEST_CMD -o $dst_dir fetch "file://${out_dir}"
-    [[ -d $dst_dir ]] && ls -l $dst_dir
-    popd > /dev/null
-}
-
-setup_test
diff --git a/fixtures/yonbanme-no-yagai-purojekuto/yonbanme-no-yagai-purojekuto.cabal b/fixtures/yonbanme-no-yagai-purojekuto/yonbanme-no-yagai-purojekuto.cabal
deleted file mode 100644
index a54d40a..0000000
--- a/fixtures/yonbanme-no-yagai-purojekuto/yonbanme-no-yagai-purojekuto.cabal
+++ /dev/null
@@ -1,11 +0,0 @@
-name: yonbanme-no-yagai-purojekuto
-version: 1.0.0
-license: BSD3
-license-file: LICENSE
-cabal-version: >= 1.18
-build-type: Simple
-
-executable yonbanme-no-yagai-purojekuto
-    build-depends: base < 5, foldl, text, turtle
-    main-is: Main.hs
-    default-language: Haskell2010
diff --git a/fixtures/gobanme-no-yagai-purojekuto/LICENSE b/haskell-overridez-tests/LICENSE
similarity index 100%
rename from fixtures/gobanme-no-yagai-purojekuto/LICENSE
rename to haskell-overridez-tests/LICENSE
diff --git a/fixtures/kyuubanme-no-purojekuto/default.nix b/haskell-overridez-tests/fixtures/kyuubanme-no-purojekuto/default.nix
similarity index 70%
rename from fixtures/kyuubanme-no-purojekuto/default.nix
rename to haskell-overridez-tests/fixtures/kyuubanme-no-purojekuto/default.nix
index 5597b9a..35cc070 100644
--- a/fixtures/kyuubanme-no-purojekuto/default.nix
+++ b/haskell-overridez-tests/fixtures/kyuubanme-no-purojekuto/default.nix
@@ -1,9 +1,10 @@
 let
-  overridez = import ./nix/haskell-overridez.nix;
+  overridez = import ./lib.nix {};
+  theOverrides = overridez.allIn ./nix;
   overlays =
     let dropTestPkgs = haskellPackagesNew: haskellPackagesOld: {
-            beam-core = null;
-            kyuubanme-no-purojekuto = haskellPackagesNew.callPackage ./nix/kyuubanme-no-purojekuto.nix {};
+            logging-effect-extra-handler = null;
+            kyuubanme-no-purojekuto = haskellPackagesNew.callPackage ./kyuubanme-no-purojekuto.nix {};
           };
     in [
       (newPkgs: oldPkgs:
@@ -12,7 +13,7 @@ let
            composeExtensionsList = fold composeExtensions (_: _: {});
          in {
            haskellPackages = oldPkgs.haskellPackages.override {
-             overrides = composeExtensionsList [dropTestPkgs (overridez.allIn ./nix)];
+             overrides = composeExtensionsList [dropTestPkgs theOverrides];
          };
       })
     ];
diff --git a/fixtures/kyuubanme-no-purojekuto/kyuubanme-no-purojekuto.cabal b/haskell-overridez-tests/fixtures/kyuubanme-no-purojekuto/kyuubanme-no-purojekuto.cabal
similarity index 89%
rename from fixtures/kyuubanme-no-purojekuto/kyuubanme-no-purojekuto.cabal
rename to haskell-overridez-tests/fixtures/kyuubanme-no-purojekuto/kyuubanme-no-purojekuto.cabal
index 90eab9c..6448de0 100644
--- a/fixtures/kyuubanme-no-purojekuto/kyuubanme-no-purojekuto.cabal
+++ b/haskell-overridez-tests/fixtures/kyuubanme-no-purojekuto/kyuubanme-no-purojekuto.cabal
@@ -6,6 +6,6 @@ cabal-version: >= 1.18
 build-type: Simple
 
 executable kyuubanme-no-purojekuto
-    build-depends: base < 5, logging-effect, prettyprinter, text
+    build-depends: base < 5, logging-effect, prettyprinter, text, logging-effect-extra-handler
     main-is: Main.hs
     default-language: Haskell2010
diff --git a/fixtures/nanabanme-no-purojekuto/default.nix b/haskell-overridez-tests/fixtures/nanabanme-no-purojekuto/default.nix
similarity index 81%
rename from fixtures/nanabanme-no-purojekuto/default.nix
rename to haskell-overridez-tests/fixtures/nanabanme-no-purojekuto/default.nix
index 15458b6..97ca77c 100644
--- a/fixtures/nanabanme-no-purojekuto/default.nix
+++ b/haskell-overridez-tests/fixtures/nanabanme-no-purojekuto/default.nix
@@ -1,15 +1,15 @@
 let
-  overridez = import ./nix/haskell-overridez.nix;
+  overridez = import ./lib.nix {};
   overlays =
     let dropTestPkgs = haskellPackagesNew: haskellPackagesOld: {
             foldl = null;
             managed = null;
             optparse-applicative = null;
             turtle = null;
-            nanabanme-no-purojekuto = haskellPackagesNew.callPackage ./nix/nanabanme-no-purojekuto.nix {};
+            nanabanme-no-purojekuto = haskellPackagesNew.callPackage ./nanabanme-no-purojekuto.nix {};
           };
     in [
-      (newPkgs: oldPkgs: = {
+      (newPkgs: oldPkgs: {
            haskellPackages = oldPkgs.haskellPackages.override {
              overrides = dropTestPkgs;
          };
diff --git a/fixtures/hachibanme-no-purojekuto/LICENSE b/haskell-overridez-tests/fixtures/template/LICENSE
similarity index 100%
rename from fixtures/hachibanme-no-purojekuto/LICENSE
rename to haskell-overridez-tests/fixtures/template/LICENSE
diff --git a/fixtures/hachibanme-no-purojekuto/default.nix b/haskell-overridez-tests/fixtures/template/default.nix
similarity index 52%
rename from fixtures/hachibanme-no-purojekuto/default.nix
rename to haskell-overridez-tests/fixtures/template/default.nix
index 9d8f1b7..5c91507 100644
--- a/fixtures/hachibanme-no-purojekuto/default.nix
+++ b/haskell-overridez-tests/fixtures/template/default.nix
@@ -1,13 +1,13 @@
 let
-  overridez = import ./nix/haskell-overridez.nix;
-  jibunNo = import ./nix/indirect_import.nix;
+  overridez = import ./lib.nix {};
+  theOverrides = overridez.allIn ./nix;
   overlays =
     let dropTestPkgs = haskellPackagesNew: haskellPackagesOld: {
             foldl = null;
             managed = null;
             optparse-applicative = null;
             turtle = null;
-            hachibanme-no-purojekuto = haskellPackagesNew.callPackage ./nix/hachibanme-no-purojekuto.nix {};
+            purojekuto-no-namae = haskellPackagesNew.callPackage ./purojekuto-no-namae.nix {};
           };
     in [
       (newPkgs: oldPkgs:
@@ -16,11 +16,13 @@ let
            composeExtensionsList = fold composeExtensions (_: _: {});
          in {
            haskellPackages = oldPkgs.haskellPackages.override {
-             overrides = composeExtensionsList [dropTestPkgs jibunNo];
+             overrides = composeExtensionsList [dropTestPkgs theOverrides];
          };
       })
     ];
-  pkgs = import <nixpkgs> { inherit overlays; };
+  nixVersion = import (./. + "/nix/18.09.nix");
+  nixpkgs = import ./nix/fetchNixPkgs.nix nixVersion;
+  pkgs = import nixpkgs { inherit overlays; };
 in
-  { hachibanme-no-purojekuto = pkgs.haskellPackages.hachibanme-no-purojekuto;
+  { purojekuto-no-namae = pkgs.haskellPackages.purojekuto-no-namae;
   }
diff --git a/haskell-overridez-tests/fixtures/template/nix/18.09.nix b/haskell-overridez-tests/fixtures/template/nix/18.09.nix
new file mode 100644
index 0000000..a85f620
--- /dev/null
+++ b/haskell-overridez-tests/fixtures/template/nix/18.09.nix
@@ -0,0 +1,4 @@
+{
+  rev = "a4c4cbb613cc3e15186de0fdb04082fa7e38f6a0";
+  sha256 = "1lagfycy2lvfc8cdxk98dz2rxjlrbmv9hj42x0x40sy66bck1w0y";
+}
\ No newline at end of file
diff --git a/haskell-overridez-tests/fixtures/template/nix/fetchNixPkgs.nix b/haskell-overridez-tests/fixtures/template/nix/fetchNixPkgs.nix
new file mode 100644
index 0000000..e04db8f
--- /dev/null
+++ b/haskell-overridez-tests/fixtures/template/nix/fetchNixPkgs.nix
@@ -0,0 +1,7 @@
+{ rev                             # The Git revision of nixpkgs to fetch
+, sha256                          # The SHA256 of the downloaded data
+}:
+builtins.fetchTarball {
+ url = "https://github.com/NixOS/nixpkgs/archive/${rev}.tar.gz";
+ inherit sha256;
+}
diff --git a/haskell-overridez-tests/fixtures/template/project.cabal b/haskell-overridez-tests/fixtures/template/project.cabal
new file mode 100644
index 0000000..0441a3f
--- /dev/null
+++ b/haskell-overridez-tests/fixtures/template/project.cabal
@@ -0,0 +1,11 @@
+name: purojekuto-no-namae
+version: 1.0.0
+license: BSD3
+license-file: LICENSE
+cabal-version: >= 1.18
+build-type: Simple
+
+executable purojekuto-no-namae
+  build-depends: base < 5, foldl, text, turtle
+  main-is: Main.hs
+  default-language: Haskell2010
diff --git a/haskell-overridez-tests/fixtures/template/project.nix b/haskell-overridez-tests/fixtures/template/project.nix
new file mode 100644
index 0000000..f737fc1
--- /dev/null
+++ b/haskell-overridez-tests/fixtures/template/project.nix
@@ -0,0 +1,7 @@
+{ pkgs ? (import <nixpkgs> {}) }:
+
+let
+  haskellPackages = pkgs.haskellPackages;
+in rec {
+  purojekuto-no-namae = haskellPackages.callCabal2nix "purojekuto-no-namae" ./. {};
+}
\ No newline at end of file
diff --git a/haskell-overridez-tests/haskell-overridez-tests.cabal b/haskell-overridez-tests/haskell-overridez-tests.cabal
new file mode 100644
index 0000000..6ef3329
--- /dev/null
+++ b/haskell-overridez-tests/haskell-overridez-tests.cabal
@@ -0,0 +1,57 @@
+name:               haskell-overridez-tests
+version:            0.10.3.1
+synopsis:           Tests haskell-overridez
+description:        A separate package for testing the haskell-overridez executable
+license:            BSD3
+license-file:       LICENSE
+author:             Tim Emiola
+maintainer:         tim.emiola@gmail.com
+category:           Distribution,nix
+homepage:           https://github.com/adetokunbo/haskell-overridez
+bug-reports:        https://github.com/adetokunbo/haskell-overridez/issues
+build-type:         Simple
+data-files:         fixtures/template/*.hs
+                    fixtures/template/LICENSE
+                    fixtures/template/*.nix
+                    fixtures/template/*.cabal
+                    fixtures/template/nix/*.nix
+                    lib.nix
+extra-source-files: README.md
+                    ChangeLog.md
+cabal-version:      2.0
+
+library
+  hs-source-dirs:     src
+  build-tool-depends: haskell-overridez:haskell-overridez
+  exposed-modules:    Test.Derivation
+                      Test.MkProjectDir
+  other-modules:      Paths_haskell_overridez_tests
+  build-depends:      base               >= 4.2 && < 5
+                    , attoparsec
+                    , containers
+                    , foldl
+                    , hspec
+                    , managed
+                    , nix-derivation
+                    , nix-paths
+                    , system-filepath
+                    , text
+                    , turtle
+  default-language:   Haskell2010
+  ghc-options:        -Wall -fwarn-tabs
+
+
+test-suite integration-tests
+  type:               exitcode-stdio-1.0
+  main-is:            Spec.hs
+  hs-source-dirs:     test
+  other-modules:      Paths_haskell_overridez_tests
+  build-depends:      base               >= 4.2 && < 5
+                    , foldl
+                    , nix-paths
+                    , hspec
+                    , haskell-overridez-tests
+                    , text
+                    , turtle
+  default-language:   Haskell2010
+  ghc-options:        -Wall -fwarn-tabs
diff --git a/haskell-overridez-tests/lib.nix b/haskell-overridez-tests/lib.nix
new file mode 100644
index 0000000..39694b7
--- /dev/null
+++ b/haskell-overridez-tests/lib.nix
@@ -0,0 +1,98 @@
+{ debug ? false, pkgs ? import <nixpkgs> {} }:
+let inherit (pkgs.lib) composeExtensions fold foldr listToAttrs mapAttrs';
+    inherit (builtins) fromJSON match pathExists readFile readDir replaceStrings toPath trace;
+
+    composeExtensionsList = fold composeExtensions (_: _: {});
+    isDir = path: pathExists (toPath (toString (path + "/.")));
+    _trace = msg: result: if debug then (trace msg result) else result;
+in
+rec {
+  combineAllIn = rootDir: otherOverrides:
+    let
+      extDir = d: (toString rootDir) + "/" + d;
+      allExtensions = [
+        (nixExprIn (extDir "nix-expr"))
+        (gitJsonIn (extDir "git-json"))
+        (optionsIn (extDir "options"))
+      ] ++ otherOverrides;
+    in
+      composeExtensionsList allExtensions;
+
+  allIn = rootDir: combineAllIn rootDir [];
+
+  nixExprIn = aDir: self: super:
+    let
+      mkOverride = f: self.callPackage (aDir + "/${f}") { };
+      toPackage = f: _: _trace "found override (nix-expr): ${f}" rec {
+        name  = builtins.replaceStrings [ ".nix" ] [ "" ] f;
+        value = _trace ("using override (nix-expr): ${name}") (mkOverride f);
+      };
+    in
+      if isDir aDir
+      then mapAttrs' toPackage (readDir (toPath aDir))
+      else _trace ("no overrides (nix-expr): directory not found ${aDir}") {};
+
+  gitJsonIn = aDir: self: super:
+    let
+      inherit (pkgs) fetchFromGitHub;
+      inherit (pkgs.lib) zipListsWith;
+
+      toGithubAttrs = src:
+        let ownerRepo = match "https://github.com/(.*)/(.*)\.git" src.url;
+            zipNV = zipListsWith (fst: snd: {name = fst; value = snd; });
+            ownerRepoAttrs = listToAttrs (zipNV ["owner" "repo"] ownerRepo);
+        in { inherit (src) rev sha256; } // ownerRepoAttrs;
+
+      applyFuncs = funcs: pkgName: foldr (g: a: g a) pkgName funcs;
+
+      readDirOverrides = fetcher: toFetchAttrs: d:
+        let filePath = n: d + "/${n}.json";
+            loadFuncs = [fetcher toFetchAttrs fromJSON readFile filePath];
+            mkOverride = n: self.callCabal2nix n (applyFuncs loadFuncs n) { };
+            toPackage = file: _: _trace "found override (git-json): ${file}" rec {
+              name  = replaceStrings [ ".json" ] [ "" ] file;
+              value = _trace ("using override (git-json): ${name}") (mkOverride name);
+            };
+        in mapAttrs' toPackage (readDir d);
+
+    in
+      if isDir aDir
+      then readDirOverrides fetchFromGitHub toGithubAttrs aDir
+      else _trace ("no overrides (git-json): was not a dir ${aDir}") {};
+
+  optionsIn = aDir: self: super:
+    let
+      inherit (builtins) attrValues filter intersectAttrs isList split;
+      inherit (pkgs.lib) mapAttrs;
+
+      supportedOptions = {
+        doJailbreak = pkgs.haskell.lib.doJailbreak;
+        dontCheck = pkgs.haskell.lib.dontCheck;
+        dontHaddock = pkgs.haskell.lib.dontHaddock;
+      };
+
+      mkOverrides = option: names: _: super:
+        let
+          f = supportedOptions.${option};
+          toPackage = name: _trace "found override (options): ${toString name}" {
+            inherit name;
+            value = _trace ("using override (options): ${toString name}") (f super.${name});
+          };
+        in
+          _trace "found option ${option} on pkgs ${toString names}"
+          listToAttrs (map toPackage names);
+
+      readOptionsOverrides = d:
+        let
+          nonEmptyNonList = x: (!(isList x)) && x != "";
+          availableOptions = intersectAttrs (readDir d) supportedOptions;
+          lines = f: filter nonEmptyNonList (split "\n" (readFile (d + "/${f}")));
+          namesPerOption = mapAttrs (opt: _: lines opt) availableOptions;
+          optionsOverrides = attrValues (mapAttrs mkOverrides namesPerOption);
+        in
+          (composeExtensionsList optionsOverrides) self super;
+    in
+      if isDir aDir
+      then readOptionsOverrides aDir
+      else _trace ("no overrides (options): was not a dir ${aDir}") {};
+}
\ No newline at end of file
diff --git a/haskell-overridez-tests/src/Test/Derivation.hs b/haskell-overridez-tests/src/Test/Derivation.hs
new file mode 100644
index 0000000..7ecb8e6
--- /dev/null
+++ b/haskell-overridez-tests/src/Test/Derivation.hs
@@ -0,0 +1,79 @@
+{-# LANGUAGE DeriveGeneric     #-}
+{-# LANGUAGE LambdaCase        #-}
+{-# LANGUAGE OverloadedStrings #-}
+{-# OPTIONS_HADDOCK prune not-home #-}
+module Test.Derivation
+  ( -- * data types
+    Dependency
+
+    -- * functions
+  , asCabalUri
+  , hasDeps
+  , mkNameOnly
+  , mkDep
+
+    -- * re-exports
+  , module Nix.Derivation
+  )
+
+where
+
+import qualified Data.Map.Strict           as Map
+import           Data.Text                 (Text)
+import qualified Data.Text                 as Text
+import           Filesystem.Path.CurrentOS (FilePath, toText)
+import           GHC.Generics              (Generic)
+import           Prelude                   hiding (FilePath)
+
+import           Nix.Derivation            (Derivation (..))
+
+
+-- | @Dependency@ is a package that may be a key in 'Derivation' 'inputDrvs'.
+data Dependency = Dependency
+  { depName    :: !Text
+  , depVersion :: !(Maybe Text)
+  } deriving (Show, Eq, Generic)
+
+
+-- | construct a dependency with name only
+mkNameOnly :: Text -> Dependency
+mkNameOnly n = Dependency n Nothing
+
+
+-- | construct a dependency with name and version
+mkDep :: Text -> Text -> Dependency
+mkDep n v = Dependency n $ Just v
+
+
+-- | Given a 'Derivation' determine if all of the given dependencies are present.
+hasDeps :: [Dependency] -> Derivation -> Bool
+hasDeps ds drv = all hasMatch ds
+  where
+    hasMatch d = any (depMatches d) drvDeps
+    drvDeps = asInputDeps drv
+
+
+depMatches :: Dependency -> Dependency -> Bool
+depMatches d1@(Dependency _ (Just _)) d2@(Dependency _ (Just _)) = d1 == d2
+depMatches (Dependency n1 _) (Dependency n2 _)                   = n1 == n2
+
+
+asInputDeps :: Derivation -> [Dependency]
+asInputDeps = map (drvToDep . fst) . Map.toAscList . inputDrvs
+
+
+drvToDep :: FilePath -> Dependency
+drvToDep = toDep . devName
+  where
+    -- N.B. this assumes that the path name is:
+    -- /nix/store/${32_CHARACTER_HASH}-${NAME}.drv
+    devName = Text.dropEnd 4 . Text.drop 44 . pathToText
+    pathToText = either id id . toText
+    toDep t = case (Text.breakOnEnd "-" t) of
+      ("", name)      -> Dependency name Nothing
+      (name, version) -> Dependency (Text.dropWhileEnd (== '-') name) $ Just version
+
+
+-- | Render as dependency as the equivalent cabal uri.
+asCabalUri :: Dependency -> Text
+asCabalUri d = "cabal://" <> depName d <> "-" <> (maybe "" id $ depVersion d)
diff --git a/haskell-overridez-tests/src/Test/MkProjectDir.hs b/haskell-overridez-tests/src/Test/MkProjectDir.hs
new file mode 100644
index 0000000..b0a666b
--- /dev/null
+++ b/haskell-overridez-tests/src/Test/MkProjectDir.hs
@@ -0,0 +1,176 @@
+{-# LANGUAGE LambdaCase        #-}
+{-# LANGUAGE OverloadedStrings #-}
+{-# OPTIONS_HADDOCK prune not-home #-}
+module Test.MkProjectDir
+  ( -- * functions
+    checkDerivation
+  , checkDerivation'
+  , mkProjectDir
+  , simpleCopy
+  , cpWithAltDir
+  )
+where
+
+import qualified Control.Foldl                 as Foldl
+import           Control.Monad.Managed         (MonadManaged)
+import qualified Data.Attoparsec.Text          as Text
+import qualified Data.Text                     as Text
+import qualified Data.Text.IO                  as Text
+import           Nix.Derivation                (Derivation, parseDerivation)
+import           Nix.Paths                     (nixInstantiate)
+import           Turtle
+import qualified Turtle                        (FilePath)
+
+import           Paths_haskell_overridez_tests
+
+
+-- | mkDerivation obtains a derivation for the given name from a copy of the
+-- template directory after running an action in it.
+mkDerivation :: MonadManaged m => HowToCopy -> IO () -> m Derivation
+mkDerivation htc action = do
+  dir <- mkProjectDir' htc
+  pushd dir
+  liftIO $ do
+    action
+    runNixInstantiate (htcName htc) dir
+
+
+-- | checkDerivation determines if the derivation created from a copy of the
+-- template directory matches a filter.
+checkDerivation :: MonadManaged m => (Derivation -> Bool) -> Text -> IO () -> m Bool
+checkDerivation checkf name action = checkf <$> mkDerivation (simpleCopy name) action
+
+
+-- | checkDerivation determines if the derivation created from a copy of the
+-- template directory matches a filter.
+checkDerivation' :: MonadManaged m => (Derivation -> Bool) -> HowToCopy -> IO () -> m Bool
+checkDerivation' checkf htc action = checkf <$> mkDerivation htc action
+
+
+runNixInstantiate :: Text -> Turtle.FilePath -> IO Derivation
+runNixInstantiate name dir = do
+  let cmd = inproc nixInstantiate' ["-A", name, (format fp dir)] empty
+  fold (lineToText <$> cmd) Foldl.head >>= \case
+    Nothing -> error $ "No derivation computed for " ++ (Text.unpack name)
+    Just drvPath -> loadDerivation $ fromText drvPath
+
+
+loadDerivation :: Turtle.FilePath -> IO Derivation
+loadDerivation drvPath = do
+  let strPath = Text.unpack $ format fp drvPath
+  drv <- Text.readFile strPath
+  case (Text.parse parseDerivation drv) of
+    Text.Done _ z -> pure z
+    _             -> error $ "failed to load a derivation from " ++ strPath
+
+
+-- | Describes how files should be copied from the template directory.
+data HowToCopy =
+  HowToCopy
+  { htcName   :: Text
+  , htcAltDir :: Maybe Turtle.FilePath
+  }
+
+
+-- | Copy files, only replacing the template project name.
+simpleCopy :: Text -> HowToCopy
+simpleCopy n = HowToCopy n Nothing
+
+
+-- | Copy files, replacing the template project name and overridez import folder.
+cpWithAltDir :: Text -> Turtle.FilePath -> HowToCopy
+cpWithAltDir n p = HowToCopy n $ Just p
+
+
+-- | Creates a project dir containing a default.nix based on the template test dir.
+mkProjectDir :: MonadManaged m => Text -> m Turtle.FilePath
+mkProjectDir name = mkProjectDir' $ simpleCopy name
+
+
+-- | Creates a project dir containing a default.nix based on the template test dir.
+mkProjectDir' :: MonadManaged m => HowToCopy -> m Turtle.FilePath
+mkProjectDir' htc@HowToCopy { htcName = name } = do
+  let cabal = fromText $ name <> ".cabal"
+      nix = fromText $ name <> ".nix"
+      projectDir = fromText name
+  dir <- mktempdir "/tmp" name
+  let nixDir = dir </> "nix"
+  mkdir nixDir
+  liftIO $ do
+    void $ cpTemplateFile dir "LICENSE"
+    mvPnameTemplate name cabal dir "project.cabal" >>= orUseAlt (projectDir </> cabal)
+    mvPnameTemplate name nix dir "project.nix" >>= orUseAlt (projectDir </> nix)
+    cpPnameTemplate htc dir "default.nix" >>= orUseAlt (projectDir </> "default.nix")
+    void $ cpProjectFile dir "lib.nix"
+    void $ cpTemplateFile nixDir "nix/fetchNixPkgs.nix"
+    void $ cpTemplateFile nixDir "nix/18.09.nix"
+    pure dir
+
+
+orUseAlt :: Turtle.FilePath -> Turtle.FilePath -> IO ()
+orUseAlt alt dst = do
+  let altPath = encodeString $ "fixtures" </> alt
+  fullAltPath <- decodeString <$> getDataFileName altPath
+  hasReplacement <- testfile fullAltPath
+  when (hasReplacement) $ cp fullAltPath dst
+
+
+-- | Copy a fixture template file to a new directory.
+cpTemplateFile :: Turtle.FilePath -> Prelude.FilePath -> IO Turtle.FilePath
+cpTemplateFile dir name = cpProjectFile dir ("fixtures/template/" ++ name)
+
+
+-- | Copy a fixture template file to a new directory.
+cpProjectFile :: Turtle.FilePath -> Prelude.FilePath -> IO Turtle.FilePath
+cpProjectFile dir name = do
+  raw <- decodeString <$> (getDataFileName name)
+  let p = dir </> (filename raw)
+  cp raw p
+  pure p
+
+
+-- | Copy a template file updating as indicated by HowToCopy.
+cpPnameTemplate :: HowToCopy -> Turtle.FilePath -> Prelude.FilePath -> IO Turtle.FilePath
+cpPnameTemplate htc =
+  let
+    HowToCopy { htcName = name, htcAltDir = mbAlt } = htc
+    justName = replacePname name
+    andNixDir = maybe id replaceNixDir mbAlt
+  in
+    sedMvTemplateFile filename (andNixDir . justName)
+
+
+-- | Copy a template file replacing the project name.
+mvPnameTemplate
+  :: Text
+  -> Turtle.FilePath
+  -> Turtle.FilePath
+  -> Prelude.FilePath
+  -> IO Turtle.FilePath
+mvPnameTemplate t newName = sedMvTemplateFile (const newName) (replacePname t)
+
+
+-- | Copy a template file, using a renamer function to determine its final name.
+sedMvTemplateFile
+  :: (Turtle.FilePath -> Turtle.FilePath)
+  -> (Shell Line -> Shell Line)
+  -> Turtle.FilePath
+  -> Prelude.FilePath
+  -> IO Turtle.FilePath
+sedMvTemplateFile rename updates dir name = do
+  raw <- decodeString <$> (getDataFileName $ "fixtures/template/" ++ name)
+  let p = dir </> rename raw
+  output p $ updates $ input raw
+  pure p
+
+
+replacePname :: Text -> Shell Line -> Shell Line
+replacePname t = sed $ (fmap (const t) $ Turtle.text "purojekuto-no-namae")
+
+
+replaceNixDir :: Turtle.FilePath -> Shell Line -> Shell Line
+replaceNixDir n = sed $ (fmap (const $ format fp n) $ Turtle.text "./nix")
+
+
+nixInstantiate' :: Text
+nixInstantiate' = Text.pack nixInstantiate
diff --git a/haskell-overridez-tests/test/Spec.hs b/haskell-overridez-tests/test/Spec.hs
new file mode 100644
index 0000000..dad9312
--- /dev/null
+++ b/haskell-overridez-tests/test/Spec.hs
@@ -0,0 +1,132 @@
+{-# LANGUAGE OverloadedStrings #-}
+
+import           Test.Hspec
+import           Turtle
+
+import           System.Exit       (ExitCode)
+import           Test.Derivation   (Dependency, asCabalUri, hasDeps, mkDep,
+                                    mkNameOnly)
+import           Test.MkProjectDir (checkDerivation, cpWithAltDir, checkDerivation')
+
+
+main :: IO ()
+main = hspec $ do
+  describe "haskell-overridez" $ do
+    context "using nix-exprs generated via cabal2nix" $ do
+      it "should create an overlay from https urls" $ do
+        let
+          setup = do
+            hoz ["--flag-override", "DontCheck", optParseUri]
+            hoz ["--flag-override", "DoJailbreak", turtleUri]
+            hoz ["--flag-override", "DoJailbreak", foldUri]
+          checkDrv = hasDeps $ map mkNameOnly ["turtle", "foldl"]
+          theTest = with (checkDerivation checkDrv "gobanme-no-purojekuto" setup) pure
+        theTest `shouldReturn` True
+
+      it "should create an overlay from cabal:// urls" $ do
+        let
+          setup = do
+            hoz ["--flag-override", "DontCheck", asCabalUri optParseDep]
+            hoz ["--flag-override", "DoJailbreak", asCabalUri foldlDep]
+            hoz ["--flag-override", "DoJailbreak", asCabalUri turtleDep]
+          checkDrv = hasDeps [foldlDep, turtleDep]
+          theTest = with (checkDerivation checkDrv "yonbanme-no-purojekuto" setup) pure
+        theTest `shouldReturn` True
+
+      it "should create an overlay from a github subdir repo" $ do
+        let
+          name = "kyuubanme-no-purojekuto"
+          subpath = "logging-effect-extra-handler"
+          setup = hoz [leExtraUri, "--", "--subpath", subpath]
+          checkDrv = hasDeps $ map mkNameOnly [subpath]
+          theTest = with (checkDerivation checkDrv name setup) pure
+        theTest `shouldReturn` True
+
+    context "using git json generated via nix-prefetch-git" $ do
+      it "should create an overlay from github repo names" $ do
+        let
+          -- can't use -g with optparse-applicative or foldl, this makes
+          -- cabal2nix infinitely recurse when converting json to nix-expr
+          setup = do
+            hoz [ "--flag-override", "DontCheck", optParseUri]
+            hoz [ "--flag-override", "DoJailbreak", "-g"
+                , "Gabriel439/Haskell-Turtle-Library"
+                ]
+            hoz [ "--flag-override", "DoJailbreak", foldUri]
+          checkDrv = hasDeps $ map mkNameOnly ["turtle", "foldl"]
+          theTest = with (checkDerivation checkDrv "rokubanme-no-purojekuto" setup) pure
+        theTest `shouldReturn` True
+
+    context "using fetched config" $ do
+      it "should create an overlay from config in a repo main folder" $ do
+        let
+          name = "ichibanme-no-yagai-purojekuto"
+          nixDir = "./nix/github.com/adetokunbo/example-fetched-haskell-overridez"
+          setup = hoz ["fetch", exGithubUri]
+          checkDrv = hasDeps $ map mkNameOnly ["turtle", "foldl"]
+          copyRule = cpWithAltDir name nixDir
+          theTest = with (checkDerivation' checkDrv copyRule setup) pure
+        theTest `shouldReturn` True
+
+      it "should create an overlay from config in a repo sub directory" $ do
+        let
+          name = "gobanme-no-yagai-purojekuto"
+          nixDir = "./nix/github.com/adetokunbo/example-fetched-haskell-overridez"
+                   </> "subdir-root" </> "a-subdir"
+          setup = hoz ["fetch", "--subpath", "subdir-root/a-subdir", exGithubUri]
+          checkDrv = hasDeps $ map mkNameOnly ["turtle", "foldl"]
+          copyRule = cpWithAltDir name nixDir
+          theTest = with (checkDerivation' checkDrv copyRule setup) pure
+        theTest `shouldReturn` True
+
+    context "saving to an alternate output directory" $ do
+      it "should create an overlay from github https:// urls" $ do
+        let
+          name = "hachibanme-no-purojekuto"
+          setup altDir = do
+            hoz' altDir ["--flag-override", "DontCheck", optParseUri]
+            hoz' altDir ["--flag-override", "DoJailbreak", turtleUri]
+            hoz' altDir ["--flag-override", "DoJailbreak", foldUri]
+          checkDrv = hasDeps $ map mkNameOnly ["turtle", "foldl"]
+          theTest = flip with pure $ do
+            altDir <- mktempdir "/tmp" $ name <> "-alt"
+            let copyRule = cpWithAltDir name $ altDir </> "nix"
+            checkDerivation' checkDrv copyRule $ setup altDir
+        theTest `shouldReturn` True
+
+    context "when the haskell-overridez functions are not used " $ do
+      it "should fail to create an overlay" $ do
+        let
+          setup = do
+            hoz ["--flag-override", "DontCheck", asCabalUri optParseDep]
+            hoz ["--flag-override", "DoJailbreak", asCabalUri foldlDep]
+            hoz ["--flag-override", "DoJailbreak", asCabalUri turtleDep]
+          checkDrv = hasDeps [foldlDep, turtleDep]
+          theTest = with (checkDerivation checkDrv "nanabanme-no-purojekuto" setup) pure
+        theTest `shouldThrow` anyExitcode
+
+
+hoz :: MonadIO io => [Text] -> io ()
+hoz args = procs "haskell-overridez" args empty
+
+
+hoz' :: MonadIO io => Turtle.FilePath -> [Text] -> io ()
+hoz' altDir args = hoz $ args <> ["-o", format fp altDir]
+
+
+turtleUri, foldUri, optParseUri, leExtraUri, exGithubUri :: Text
+turtleUri   = "https://github.com/Gabriel439/Haskell-Turtle-Library"
+foldUri     = "https://github.com/Gabriel439/Haskell-Foldl-Library"
+optParseUri = "https://github.com/pcapriotti/optparse-applicative"
+leExtraUri  = "https://github.com/jship/logging-effect-extra"
+exGithubUri = "https://github.com/adetokunbo/example-fetched-haskell-overridez"
+
+
+turtleDep, foldlDep, optParseDep :: Dependency
+turtleDep = mkDep "turtle" "1.5.12"
+foldlDep = mkDep "foldl" "1.4.5"
+optParseDep = mkDep "optparse-applicative" "0.14.2.0"
+
+
+anyExitcode :: Selector ExitCode
+anyExitcode = const True
diff --git a/test.sh b/test.sh
index ee4de95..07201b1 100755
--- a/test.sh
+++ b/test.sh
@@ -99,4 +99,5 @@ _add_current_project_to_nix() {
     sed -i'.bak' -e 's|src = ./.|src = ../.|' $nix_file
 }
 
-test "$@"
+echo "DEPRECATED: instead of test.sh, use 'nix-shell --run 'cabal new-test haskell-overridez-tests'"
+# test "$@"