JUnit, tearDown, and uncaught exceptions

I know this, I've known it for a while, and still I stumble over it.

I tend to generally declare my JUnit test cases as

public void testXXX()
  throws Exception
{
}

Within my test case code, I then typically don't catch any exceptions, unless I'm specifically testing that a particular expected exception is thrown. Instead, I simply allow any unexpected exceptions to be thrown out of the test case, and caught by the JUnit infrastructure, which decides that a test case which terminated with an uncaught exception is an error, and JUnit reports the uncaught exception in the output.

However, there is a gotcha, and it involves the tearDown method. If a particular test suite uses the setUp/tearDown paradigm to perform common initialization and termination functions, then it is crucial that these methods themselves must be cautious with respect to exceptions.

Because if:

• your test case terminates with an uncaught exception,
  
• and then your tearDown method terminates with an uncaught exception,
  

then it is the tearDown exception which "wins"; i.e., it is the exception which is shown in the JUnit output.

This can completely fool you into a wild goose chase of looking at the wrong problem.

In a way, I think this is a mistake in JUnit; I wish it reported the uncaught exception from the test case in preference to the uncaught exception from tearDown, or even better I wish it reported both exceptions.

But, for now, the best thing to do is to ensure that your tearDown methods are extremely careful, and never terminate with uncaught exceptions.