How to Mock a Static Method

More and more i encounter places and people that still insists that static methods cant be mocked and therefore makes unit testing code which uses them harder.

Here's a very short example on how a static method CAN be mocked using the proper toolset in .Net, Java and C++. The ability to mock static methods is part of the mocking libraries I am using (Isolator for .Net, PowerMock for Jave and MockItNow for C++).

Design wise, I do NOT claim that using static methods is a good practice. In fact I am NOT a design expert, and therefore I don't have any sort of claim on what are good design practice and what are bad design practice. What I do claim is that unit tests can be written to code even if it does use static methods.

In all the examples I'll be using a class which looks something like this:

public class ClassWithStaticMethod
{
   public static int StaticMethodReturnFive()
   {
       return 5;
   }
}

.NET

[TestMethod()]
[Isolated]
public void MockStaticMethodToReturnSix()
{
   Isolate.WhenCalled(() => ClassWithStaticMethod.StaticMethodReturnFive()).WillReturn(6);

   int actual = ClassWithStaticMethod.StaticMethodReturnFive();
   Assert.AreEqual(6, actual);
}

Java

@Test
@PrepareForTest(ClassWithStaticMethod.class)
public void MockStaticMethodToReturnSix()
{
    mockStatic(ClassWithStaticMethod.class);
    expect(ClassWithStaticMethod.StaticMethodReturnFive()).andReturn(6);
    replay(ClassWithStaticMethod.class);

    int actual = ClassWithStaticMethod.StaticMethodReturnFive();
    Assert.assertEquals(6, actual);
}

C++

TEST(MockStaticMethodToReturnSix)
{
   Mocker mocker;

   ClassWithStaticMethod* fake = new ClassWithStaticMethod();
   REGISTER(ClassWithStaticMethod::StaticMethodReturnFive);
   RECORD
   {
       EXPECT_RETURN_ALWAYS(ClassWithStaticMethod::StaticMethodReturnFive(),6);
   }

   int actual = ClassWithStaticMethod::StaticMethodReturnFive();
   CHECK(6==actual);
}

Posted in: C++,Java,Mocking,tips,Typemock,Unit Tests