JUnit 4.11 - What's new? Parameterized descriptions

JUnit 4.11 is a major release of the popular testing framework. Amongst the changes were changes to how Parameterized tests are described by the various runners (maven surefire, Eclipse etc).

With JUnit 4.10, when you ran a Parameterized test, all you got in the description was an integer index, which wasn’t very useful. Taking the following test class as an example:

@RunWith(Parameterized.class)
public class ParameterizedTest {
  @Parameters
  public static Iterable<Object[]> data() {
    return Arrays.asList(new Object[][] {
      { 0, 0 },
      { 1, 1 },
      { 2, 1 },
    });
  }

  private int input;
  private int expected;

  public ParameterizedTest(int input, int expected) {
    this.input = input;
    this.expected = expected;
  }

  @Test public void test() {
    assertEquals(expected, Fibonacci.compute(input));
  }

  public static void main(String[] args) {
    RunListener runListener = new RunListener() {
      public void testFailure(Failure failure) throws Exception {
        System.out.println("testFailure " + failure.getDescription().getDisplayName());
      }
    };
    JUnitCore jUnitCore = new JUnitCore();
    jUnitCore.addListener(runListener);
    jUnitCore.run(ParameterizedTest.class);
  }
}

When we run this (as a main method), we get the following output:

testFailure test[0](uk.co.farwell.ParameterizedTest)
testFailure test[1](uk.co.farwell.ParameterizedTest)
testFailure test[2](uk.co.farwell.ParameterizedTest)

The output isn’t very useful when we’re debugging tests, especially if there are lots of them. So, JUnit 4.11 allows the description of the test to be modified by adding a annotation parameter:

@Parameters(name = "{index}: fib({0}) should be {1}")
public static Iterable<Object[]> data() {
  return Arrays.asList(new Object[][] {
    { 0, 0 },
    { 1, 1 },
    { 2, 1 },
  });
}

The {0} is replaced by the first parameter for the test, and so on. Now the description is much more, well, descriptive:

testFailure test[0: fib(0) should be 0](uk.co.farwell.ParameterizedTest)
testFailure test[1: fib(1) should be 1](uk.co.farwell.ParameterizedTest)
testFailure test[2: fib(2) should be 1](uk.co.farwell.ParameterizedTest)

However, when running with the junit runner in Eclipse, you need to be careful. When it creates the descriptions for the test classes, it uses (approximately) ‘uk.co.farwell.ParameterizedTest(test)’. It then uses the name of the test to work out which class and method to jump to when you double click on the test in the junit view. So if, as above, we use parentheses in the description, this doesn’t work. It also screws up the display of the test name in the junit view.

The moral of the story: Don’t use parentheses in your descriptions for parameterized tests.