organising junit tests that expect an exception

Question

I have a class which internally uses a 2D array ,and exposes a processItem(int i,int j) method as given below. The method uses 1-based index and has a constructor which takes an int value (say N) as the 2D array size. So, for N=10, the value of i and j should be 1 to N .If the method is called with i or j less than 1 or greater than 10 ,the method would throw an IndexOutOfBoundsException .

In my unit test ,I want to call the method with i,j values

(0,4),(11,3),(3,0),(3,11)

and these calls should throw IndexOutOfBoundsException

How do I organise the tests, do I have to write 1 separate test for each i,j pair? Or is there a better way to organise them?

class MyTest{
  MyTestObj testobj;
  public MyTest(){
      testobj = new MyTestObj(10);
  }
  @Test(expected=IndexOutOfBoundsException.class)
  public void test1(){
      testobj.processItem(0,4);
  }

  @Test(expected=IndexOutOfBoundsException.class)
  public void test2(){
      testobj.processItem(11,3);
  }

  @Test(expected=IndexOutOfBoundsException.class)
  public void test3(){
      testobj.processItem(3,0);
  }

  @Test(expected=IndexOutOfBoundsException.class)
  public void test4(){
      testobj.processItem(3,11);
  }
..
}

Answer 1

If they are completely independent then write independent tests, but if they are closely related (looks like it) then just have a single test with the four calls, each call wrapped in a try-catch, and a fail('exception expected') after each call. As it was done in junit 3.

Answer 2

Rather than creating separate methods just for specifying separate arguments to your method under test. Use JUnit Parameterized Test . Here is an example for Fibonacci series.

So you will be able to use this in your implementation and expect ArrayIndexOutOfBounds for the single test method.

@RunWith(Parameterized.class)
public class FibonacciTest {
    @Parameters
    public static Collection<Object[]> data() {
        return Arrays.asList(new Object[][] {
                Fibonacci,
                { { 0, 0 }, { 1, 1 }, { 2, 1 }, { 3, 2 }, { 4, 3 }, { 5, 5 },
                        { 6, 8 } } });
    }

    private int fInput;

    private int fExpected;

    public FibonacciTest(int input, int expected) {
        fInput= input;
        fExpected= expected;
    }

    @Test
    public void test() {
        assertEquals(fExpected, Fibonacci.compute(fInput));
    }
}