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Uncovered not always bad 35

Posted by Brett Schuchert Thu, 31 May 2007 05:10:00 GMT

Let’s say for the sake of argument that you are:
  • Using a code coverage tool such as Cobertura, Emma
  • You are actually looking at the coverage of your tests (say you’re looking for stale code in our unit tests – [and you’re thinking gosh, I wish I had some unit tests so I could have some unused code in my unit tests])
  • You are testing that unit under test generates an exception
In JUnit 4 we might write the following: 
@Test(expected=RuntimeException.class)
public void methodThatWeExpectAnException() {
    throw new RuntimeException();
}

This test will pass. Yes it’s trivial, of course it would pass. (In reality the single line of code would instead send a message to some object that ultimately would need to generate a RuntimeException for a “real” test to pass.) Fine. That’s not the point.

So what’s the problem with this? Nothing, except that some coverage tools will report the last “line” (the close curly-brace) as not being covered since we did not exit the method cleanly.

Here’s a way to rewrite the above test so that you can assure coverage: 
@Test
public void methodThatWeExpectWillThrowAnException() {
    boolean expectedThrown = false;

    try {
        throw new RuntimeException();
    } catch (RuntimeException e) {
        expectedThrown = true;
    }

    assertTrue(expectedThrown);
}

This version is a bit longer, isn’t it?

Here are some comments I’d like to hear from you:
  • Is it any better?
  • Does is express our intent any better?
  • Isn’t it just silly to run coverage tools on your test code?
  • Is anybody having Pascal flashbacks? (If you don’t get this question…you poor &*$^@~).