Mocking System.Enum

[Christian]

hello,
I try to create a mock for System.Enum. That works for all public static methods of the System.Enum class (i.e. Enum.GetValues). But I have no idea how to set up the mock for the ToString() method of the Enum object.
(all C# .NET)

method:

public static void TestThis(ListControl ctrl, Type enumType, Enum enumItem= null)
{
    int[] itemValues = Enum.GetValues(enumType).ToArray<int>();
    string[] itemNames = Enum.GetNames(enumType);

    string s = enumItem.ToString();
}

mock:

Mock.SetupStatic(typeof(Enum), Behavior.Strict);

Mock.Arrange(() => Enum.GetValues(Arg.IsAny<Type>())).Returns(new int[] { 1, 2, 3 });

Mock.Arrange(() => Enum.GetNames(Arg.IsAny<Type>())).Returns(new string[] { "1", "2", "3" });

 
//--- this causes an exception (Cannot create mock for type due to CLR limitations.)

Enum e = Mock.Create<Enum>();

Mock.Arrange(() => e.ToString()).IgnoreArguments().IgnoreInstance().Returns("2");
//---

//--- in that case null is returned instead of "2"; compiler never steps into the mocked "returns"

TestEnum e = Mock.Create<TestEnum>();

Mock.Arrange(() => e.ToString()).IgnoreArguments().IgnoreInstance().Returns("2");
//---

DropDownList ddlTestList = new DropDownList();
TestThis(ddlTestList, typeof(TestEnum), TestEnum.Empty)

[Stefan]

Hi Christian,

It's simply impossible to arrange the instance methods of System.ValueType and System.Enum. Like the exception says, it's a limitation of the CLR.

As a rule of thumb, if you need to mock Enum.ToString(), you might want to reconsider what is it that you're doing... because you might be doing something that you will eventually hate to provide support for.

Regards,
Stefan
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