Re #7670: WIP: test case for #7248 (#7702)

* Re #7670: WIP: test case for #7248

Two problems remaining:
- Warning output is not recorded in the golden value.
- The correct warning is not produced yet.

Current warning:

    Warning: No remote package servers have been specified. Usually you would have one specified in the config file.

* Re #7670: completed: test case for #7248

* Re #7670: update test output witnessing the fix of #7248

* Re #7670: use cmd 'get' instead of 'unpack'

* Re #7670: rename test subdir 'Unpack' to 'Get'

* Re #7670: use .invalid domain in test

Co-authored-by: Francesco Gazzetta <[email protected]>

cabal-testsuite/PackageTests/Get/T7248/cabal.config

@@ -0,0 +1,4 @@
+-- This config file contains a bogus repository by intention.
+
+repository repo.invalid
+  url: http://repo.invalid/

cabal-testsuite/PackageTests/Get/T7248/cabal.out

@@ -0,0 +1,5 @@
+# cabal get
+Warning: <ROOT>/cabal.config: Unrecognized stanza on line 3
+Warning: The package list for 'repo.invalid' does not exist. Run 'cabal update' to download it.
+Error: cabal: There is no package named 'a-b-s-e-n-t'. 
+You may need to run 'cabal update' to get the latest list of available packages.

cabal-testsuite/PackageTests/Get/T7248/cabal.test.hs

@@ -0,0 +1,15 @@
+-- 2021-10-06, issue #7248
+--
+-- Purpose of this test:
+-- Make sure that ordinary user communication does not contain 'Show'ed internal structures.
+--
+-- This is a golden value test that reports the produced error message.
+-- Needs to be checked manually whether it meets expectations.
+
+import Test.Cabal.Prelude
+main = cabalTest $
+  fails $
+  cabalG
+    [ "--config-file", "cabal.config" ]
+    "get"
+    [ "a-b-s-e-n-t" ]

cabal-testsuite/src/Test/Cabal/Prelude.hs

@@ -276,7 +276,15 @@ cabalGArgs global_args cmd args input = do
     -- overwritable
     when (cmd == "v1-freeze") requireHasSourceCopy
     let extra_args
-          | cmd `elem` ["v1-update", "outdated", "user-config", "man", "v1-freeze", "check"]
+          | cmd `elem`
+              [ "v1-update"
+              , "outdated"
+              , "user-config"
+              , "man"
+              , "v1-freeze"
+              , "check"
+              , "get", "unpack"
+              ]
           = [ ]
 
           -- new-build commands are affected by testCabalProjectFile