Friday, October 07, 2005

Testing protected methods with JUnit 4

One of the pains of JUnit is testing protected methods. Public methods offer no impediment to testing, and private methods in well-designed classes can be ignored as implementation details called by the public methods. But protected methods are important for frameworks and central to the Template Method pattern; they need testing.

The most common ways to test protected methods that I've seen are to invoke the protected method with reflection, to use a private inner helper class which extends the class under test, and similarly to extend the class under test and change the access of the protected methods to public. All have their drawbacks.

Enter JUnit 4. No longer must test classes extend TestCase. Using annotations, the test framework finds and runs your test methods without inheritance, and static imports keep calls to assertTrue and friends looking clean and tidy.

Your test class itself can extend the class under test and access the protected methods without the need for reflection or a second, helper class. This is another blow struck for small, clean code thanks to JDK 5.

UPDATE: As Sam in the comments pointed out, one could just put the tests in the same package as the class under test. For silly reasons, I left this out of the list of workarounds.

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