Remove doubled exception message from nunit

src/FsUnit.NUnit/FsUnitTyped.fs

@@ -5,15 +5,17 @@ open NUnit.Framework
 open System.Collections.Generic
 
 [<AutoOpen>]
-
 module TopLevelOperators =
+
     [<DebuggerStepThrough>]
     let shouldEqual (expected: 'a) (actual: 'a) =
-        Assert.That(actual, FsUnit.Equality.IsEqualTo(expected), sprintf "Expected: %A\nActual: %A" expected actual)
+        FsUnit.TopLevelOperators.FSharpCustomMessageFormatter() |> ignore
+        Assert.That(actual, FsUnit.Equality.IsEqualTo(expected))
 
     [<DebuggerStepThrough>]
     let shouldNotEqual (expected: 'a) (actual: 'a) =
-        Assert.That(actual, FsUnit.Equality.IsNotEqualTo(expected), sprintf "Expected: %A\nActual: %A" expected actual)
+        FsUnit.TopLevelOperators.FSharpCustomMessageFormatter() |> ignore
+        Assert.That(actual, FsUnit.Equality.IsNotEqualTo(expected))
 
     [<DebuggerStepThrough>]
     let shouldContain (x: 'a) (y: 'a seq) =

tests/FsUnit.NUnit.Test/typed.shouldEqualTests.fs

@@ -4,17 +4,17 @@ open System.Collections.Immutable
 
 open NUnit.Framework
 open FsUnitTyped
+open FsUnit
+open System
 
 type AlwaysEqual() =
     override this.Equals(other) = true
     override this.GetHashCode() = 1
 
-
 type NeverEqual() =
     override this.Equals(other) = false
     override this.GetHashCode() = 1
 
-
 [<TestFixture>]
 type ``shouldEqual Tests``() =
     let anObj = new obj()
@@ -75,6 +75,34 @@ type ``shouldEqual Tests``() =
     member __.``None should equal None``() =
         None |> shouldEqual None
 
+    [<Test>]
+    member __.``Error "Foo" should equal Error "Foo"``() =
+        Error "Foo" |> shouldEqual(Error "Foo")
+
+    [<Test>]
+    member __.``Error "Foo" should equal fails and have same message``() =
+        (fun () -> Error "Foo" |> shouldEqual(Error "Bar"))
+        |> Assert.Throws<AssertionException>
+        |> fun e ->
+            e.Message
+            |> should
+                equal
+                   (sprintf "  Expected: Error \"Bar\" or Error \"Bar\"%s  But was:  Error \"Foo\"%s" Environment.NewLine Environment.NewLine)
+
+    [<Test>]
+    member __.``Error "Foo" should not equal Error "Bar"``() =
+        Error "Foo" |> shouldNotEqual(Error "Bar")
+
+    [<Test>]
+    member __.``Error "Foo" should not equal Error "Bar" fails and have same message``() =
+        (fun () -> Error "Foo" |> shouldNotEqual(Error "Foo"))
+        |> Assert.Throws<AssertionException>
+        |> fun e ->
+            e.Message
+            |> should
+                equal
+                   (sprintf "  Expected: not Error \"Foo\" or Error \"Foo\"%s  But was:  Error \"Foo\"%s" Environment.NewLine Environment.NewLine)
+
     [<Test>]
     member this.``structural equality``() =
         let actualList: char list = []