Where should I test methods on an abstract class?

I have an abstract class that defines some methods. This class has two su开发者_运维百科bclasses.

Should I create a fake subclass just for testing, or should I test the methods through the subclasses' tests? Testing through the subclasses seems more natural, but then I'd have to duplicate the test code between the 2 subclasses' tests.

What do you guys think?

You don't have to duplicate your test code - you can write your test methods so that they accept a parameter.

Since most test frameworks don't support tests that take parameters you can add a little wrapper that calls your parameterized test method with a specific instance. You can now easily choose whether it makes sense to call your test just once with some specific base class, or have multiple tests of the same method - one test for each of the possible base classes. Since only a thin wrapper needs to be added for each new test, there is very little code duplication.

void TestSomething(AbstractClass foo)
{
    // Your test code goes here.
    Assert.AreEqual(42, foo.Bar());
}

[Test]
void TestSomethingFoo1()
{
    TestSomething(new Foo1());
}

[Test]
void TestSomethingFoo2()
{
    TestSomething(new Foo2());
}

I would go for a minimal fake subclass, associating this with the Abstract Class. I like to think that the Abstract class is properly tested no matter what happens to any of the Concrete instantiations. This does assume that the code in the Abstract class is non-trivial and writing the fake class is not dispropoartionate work - with mocks I think this will usually be the case.