From 063e38533390613140ab9464f82ca7f098616514 Mon Sep 17 00:00:00 2001
From: Abel Braaksma <abel.online@xs4all.nl>
Date: Thu, 24 Nov 2022 22:28:27 +0100
Subject: [PATCH] Add tests for `TaskSeq.singleton`

---
 .../FSharp.Control.TaskSeq.Test.fsproj        |  1 +
 .../TaskSeq.Singleton.Tests.fs                | 80 +++++++++++++++++++
 src/FSharp.Control.TaskSeq.Test/TestUtils.fs  |  5 ++
 3 files changed, 86 insertions(+)
 create mode 100644 src/FSharp.Control.TaskSeq.Test/TaskSeq.Singleton.Tests.fs

diff --git a/src/FSharp.Control.TaskSeq.Test/FSharp.Control.TaskSeq.Test.fsproj b/src/FSharp.Control.TaskSeq.Test/FSharp.Control.TaskSeq.Test.fsproj
index 0d0b6019..ee7c16c8 100644
--- a/src/FSharp.Control.TaskSeq.Test/FSharp.Control.TaskSeq.Test.fsproj
+++ b/src/FSharp.Control.TaskSeq.Test/FSharp.Control.TaskSeq.Test.fsproj
@@ -39,6 +39,7 @@
     <Compile Include="TaskSeq.Map.Tests.fs" />
     <Compile Include="TaskSeq.OfXXX.Tests.fs" />
     <Compile Include="TaskSeq.Pick.Tests.fs" />
+    <Compile Include="TaskSeq.Singleton.Tests.fs" />
     <Compile Include="TaskSeq.Tail.Tests.fs" />
     <Compile Include="TaskSeq.ToXXX.Tests.fs" />
     <Compile Include="TaskSeq.Zip.Tests.fs" />
diff --git a/src/FSharp.Control.TaskSeq.Test/TaskSeq.Singleton.Tests.fs b/src/FSharp.Control.TaskSeq.Test/TaskSeq.Singleton.Tests.fs
new file mode 100644
index 00000000..ea2d2368
--- /dev/null
+++ b/src/FSharp.Control.TaskSeq.Test/TaskSeq.Singleton.Tests.fs
@@ -0,0 +1,80 @@
+module TaskSeq.Tests.Singleton
+
+open System.Threading.Tasks
+open Xunit
+open FsUnit.Xunit
+open FsToolkit.ErrorHandling
+
+open FSharp.Control
+
+module EmptySeq =
+
+    [<Theory; ClassData(typeof<TestEmptyVariants>)>]
+    let ``TaskSeq-singleton with empty has length one`` variant =
+        taskSeq {
+            yield! TaskSeq.singleton 10
+            yield! Gen.getEmptyVariant variant
+        }
+        |> TaskSeq.exactlyOne
+        |> Task.map (should equal 10)
+
+module Other =
+    [<Fact>]
+    let ``TaskSeq-singleton creates a sequence of one`` () =
+        TaskSeq.singleton 42
+        |> TaskSeq.exactlyOne
+        |> Task.map (should equal 42)
+
+    [<Fact>]
+    let ``TaskSeq-singleton can be yielded multiple times`` () =
+        let singleton = TaskSeq.singleton 42
+
+        taskSeq {
+            yield! singleton
+            yield! singleton
+            yield! singleton
+            yield! singleton
+        }
+        |> TaskSeq.toList
+        |> should equal [ 42; 42; 42; 42 ]
+
+    [<Fact>]
+    let ``TaskSeq-singleton with isEmpty`` () =
+        TaskSeq.singleton 42
+        |> TaskSeq.isEmpty
+        |> Task.map (should be False)
+
+    [<Fact>]
+    let ``TaskSeq-singleton with append`` () =
+        TaskSeq.singleton 42
+        |> TaskSeq.append (TaskSeq.singleton 42)
+        |> TaskSeq.toList
+        |> should equal [ 42; 42 ]
+
+    [<Theory; ClassData(typeof<TestImmTaskSeq>)>]
+    let ``TaskSeq-singleton with collect`` variant =
+        Gen.getSeqImmutable variant
+        |> TaskSeq.collect TaskSeq.singleton
+        |> verify1To10
+
+    [<Fact>]
+    let ``TaskSeq-singleton does not throw when getting Current before MoveNext`` () = task {
+        let enumerator = (TaskSeq.singleton 42).GetAsyncEnumerator()
+        let defaultValue = enumerator.Current // should return the default value for int
+        defaultValue |> should equal 0
+    }
+
+    [<Fact>]
+    let ``TaskSeq-singleton does not throw when getting Current after last MoveNext`` () = task {
+        let enumerator = (TaskSeq.singleton 42).GetAsyncEnumerator()
+        let! isNext = enumerator.MoveNextAsync()
+        isNext |> should be True
+        let value = enumerator.Current // the first and only value
+        value |> should equal 42
+
+        // move past the end
+        let! isNext = enumerator.MoveNextAsync()
+        isNext |> should be False
+        let defaultValue = enumerator.Current // should return the default value for int
+        defaultValue |> should equal 0
+    }
diff --git a/src/FSharp.Control.TaskSeq.Test/TestUtils.fs b/src/FSharp.Control.TaskSeq.Test/TestUtils.fs
index 91baf383..dd4873b3 100644
--- a/src/FSharp.Control.TaskSeq.Test/TestUtils.fs
+++ b/src/FSharp.Control.TaskSeq.Test/TestUtils.fs
@@ -141,6 +141,11 @@ module TestUtils =
         |> TaskSeq.toArrayAsync
         |> Task.map (Array.isEmpty >> should be True)
 
+    let verify1To10 ts =
+        ts
+        |> TaskSeq.toArrayAsync
+        |> Task.map (should equal [| 1..10 |])
+
     /// Delays (no spin-wait!) between 20 and 70ms, assuming a 15.6ms resolution clock
     let longDelay () = task { do! Task.Delay(Random().Next(20, 70)) }