Question

I am trying my hand at writing test cases. From what I have read, my tests should fail from the start and I should strive to make tests pass. However, I find myself writing tests checking boundaries and the exceptions they should cause:

@Test(expected=NegativeArraySizeException.class)
public void testWorldMapIntInt() {
    WorldMap w = new WorldMap(-1, -1);
}

@Test(expected=IndexOutOfBoundsException.class)
public void testGetnIntnInt() {
    WorldMap w = new WorldMap(10,10);
    Object o = w.get(-1, -1);
}

However, this test passes by default because Java will throw the exception anyway. Is there a better way to handle these kinds of expected exceptions, possibly a way that fails by default– forcing me to strive to handle these cases?

Answer 1

I agree that the style you present is not so good. The problem is that it doesn’t check where in the method the exception is thrown, so it’s possible to get false negatives.

We usually write tests for exceptions like this:

public void testWorldMapIntInt() {
    try {
        WorldMap w = new WorldMap(-1, -1);
        Assert.fail("should have thrown IndexOutOfBoundsException");
    }
    catch (IndexOutOfBoundsException e) {}
}