shim a sealed class singleton method and with MS Fakes

Question

i have a sealed class singleton Foo and its method:

    public string GetFolderPath(FooFolder folder)
    {
        IBoo boo = this.GetBoo();
        return boo.GetFolderPath(folder);
    }

and want to write a test for a method called FindFile using the GetFolderPath method like this:

    [TestMethod]
    public void FindFile()
    {   
        string expectedPath = Path.Combine(Path.GetTempPath(), "TestPath");
        using (ShimsContext.Create())
        {
            Fakes.ShimFoo.AllInstances.GetFolderPathFolder
                = () => { return "C:\\...\\Temp"; };

        }
        string actualPath = WorkflowHelper.FindFile("TestPath");
        Assert.AreEqual(expectedPath, actualPath);
    }

the problem is that i'm getting the following compilation error:

Delegate does not take 0 arguments

In an similar Question How to shim OpenFileDialog.ShowDialog method the problem is solved like this :

[TestMethod]
public void SomeTest()
{
    using (var context = ShimsContext.Create())
    {
        Nullable<bool> b2 = true;
        ShimCommonDialog.AllInstances.ShowDialog = (x) => b2;

        var sut = new Sut();

        var r = sut.SomeMethod();

        Assert.IsTrue(r);
    }
}

So i tried the same... according to the fact that GetFolderPath is a method with 1 Parameter...

next problem is that i'm getting the following compilation error:

Delegate does not take 1 arguments

So my question is:

Is it possible to shim a sealed class and particulary a singleton? And if so, what´s my mistake?

thank you in anticipation

Answer 1

Note that all shims assigned in the lifetime of ShimsContext will be destroyed after the ShimsContext is disposed.

In your sample, you are invoking WorkflowHelper.FindFile outside the using block that binds the lifetime of your ShimsContext, so the shimmed definition for Foo.GetFolderPath is no longer effective and the call to FindFile will use the original method definition.

Just move your method call inside the using block and it will work:

    using (ShimsContext.Create())
    {
        Fakes.ShimFoo.AllInstances.GetFolderPathFolder = ...; // your lambda expression

        string actualPath = WorkflowHelper.FindFile("TestPath");
    }
    Assert.AreEqual(expectedPath, actualPath);