Cover termination

Author: bartelink

src/FSharp.Control.TaskSeq.Test/TaskSeq.TakeWhile.Tests.fs

@@ -27,11 +27,42 @@ module EmptySeq =
         |> TaskSeq.toListAsync
         |> Task.map (List.isEmpty >> should be True)
 
+module Terminates =
+
+    [<Fact>]
+    let ``TaskSeq-takeWhile stops after predicate fails`` () =
+        seq { 1; 2; 3; failwith "Too far" }
+        |> TaskSeq.ofSeq
+        |> TaskSeq.takeWhile (fun x -> x <= 2)
+        |> TaskSeq.map char
+        |> TaskSeq.map ((+) '@')
+        |> TaskSeq.toArrayAsync
+        |> Task.map (String >> should equal "AB")
+
+    [<Fact>]
+    let ``TaskSeq-takeWhileAsync stops after predicate fails`` () =
+        taskSeq { 1; 2; 3; failwith "Too far" }
+        |> TaskSeq.takeWhileAsync (fun x -> task { return x <= 2 })
+        |> TaskSeq.map char
+        |> TaskSeq.map ((+) '@')
+        |> TaskSeq.toArrayAsync
+        |> Task.map (String >> should equal "AB")
+
+// This is the base condition as one would expect in actual code
+let inline cond x = x <> 6
+
+// For each of the tests below, we add a guard that will trigger if the predicate is passed items known to be beyond the
+// first failing item in the known sequence (which is 1..10)
+let inline condWithGuard x =
+    let res = cond x
+    if x > 6 then failwith "Test sequence should not be enumerated beyond the first item failing the predicate"
+    res
+
 module Immutable =
     [<Theory; ClassData(typeof<TestImmTaskSeq>)>]
     let ``TaskSeq-takeWhile filters correctly`` variant =
         Gen.getSeqImmutable variant
-        |> TaskSeq.takeWhile (fun x -> x <> 6)
+        |> TaskSeq.takeWhile condWithGuard
         |> TaskSeq.map char
         |> TaskSeq.map ((+) '@')
         |> TaskSeq.toArrayAsync
@@ -40,7 +71,7 @@ module Immutable =
     [<Theory; ClassData(typeof<TestImmTaskSeq>)>]
     let ``TaskSeq-takeWhileAsync filters correctly`` variant =
         Gen.getSeqImmutable variant
-        |> TaskSeq.takeWhileAsync (fun x -> task { return x <> 6 })
+        |> TaskSeq.takeWhileAsync (fun x -> task { return condWithGuard x })
         |> TaskSeq.map char
         |> TaskSeq.map ((+) '@')
         |> TaskSeq.toArrayAsync
@@ -50,7 +81,7 @@ module SideEffects =
     [<Theory; ClassData(typeof<TestSideEffectTaskSeq>)>]
     let ``TaskSeq-takeWhile filters correctly`` variant =
         Gen.getSeqWithSideEffect variant
-        |> TaskSeq.takeWhile (fun x -> x <> 6)
+        |> TaskSeq.takeWhile condWithGuard
         |> TaskSeq.map char
         |> TaskSeq.map ((+) '@')
         |> TaskSeq.toArrayAsync
@@ -59,7 +90,7 @@ module SideEffects =
     [<Theory; ClassData(typeof<TestSideEffectTaskSeq>)>]
     let ``TaskSeq-takeWhileAsync filters correctly`` variant =
         Gen.getSeqWithSideEffect variant
-        |> TaskSeq.takeWhileAsync (fun x -> task { return x <> 6 })
+        |> TaskSeq.takeWhileAsync (fun x -> task { return condWithGuard x })
         |> TaskSeq.map char
         |> TaskSeq.map ((+) '@')
         |> TaskSeq.toArrayAsync