Fixes #341

Expecto.Tests/Bug341.fs

@@ -0,0 +1,27 @@
+module Expecto.Bug341Test
+open Expecto
+open System.IO
+
+type TestDir =
+  { Dir: string }
+  interface System.IDisposable with
+    member x.Dispose() =
+      try
+        ()
+      with e ->
+        eprintf "Failed to delete '%s': %O" x.Dir e
+
+let createTestDir() =
+    let testFile = Path.Combine(Path.GetTempPath(), Path.GetRandomFileName())
+    Directory.CreateDirectory(testFile)
+        |> ignore<DirectoryInfo>
+    { Dir = testFile }
+
+[<Tests>]
+let tests =
+  testList "Tests" [
+    test "test" {
+      use _ = createTestDir() // <- FS0001
+      ()
+    }
+  ]

Expecto.Tests/Expecto.Tests.fsproj

@@ -12,6 +12,7 @@
     <Compile Include="FocusedTests.fs" />
     <Compile Include="FsCheckTests.fs" />
     <Compile Include="PerformanceTests.fs" />
+    <Compile Include="Bug341.fs" />
     <Compile Include="Main.fs" />
     <None Include="paket.references" />
     <ProjectReference Include="..\Expecto.Hopac\Expecto.Hopac.fsproj" />

Expecto/Expecto.fs

@@ -1304,9 +1304,9 @@ module Tests =
       try
         f disposable
       finally
-        match disposable with
-        | null -> ()
-        | disp -> disp.Dispose()
+        match box disposable with
+        | :? IDisposable as d when not (isNull d) -> d.Dispose()
+        | _ -> ()
     member __.For(sequence, f) =
       for i in sequence do f i
     member __.Combine(f1, f2) = f2(); f1