Question

I have the following class to test:

public abstract class Challenge {
    protected int id;
    protected String name;
    protected String question;

    protected Challenge(){}

    public String[] toStrings(){
        String[] s = {Integer.toString(id), name, question};
        return s; 
    }

    ...

But using this test:

@Test
public void testToStrings() throws Exception{

    String[] expectedResult1 = new String[]{"1", "a", "b"};

    String[] obtainedResult1 = null;

    Challenge challengeMock = PowerMockito.mock(Challenge.class);
    challengeMock.id = 1;
    challengeMock.name = "a";
    challengeMock.question = "b";

    obtainedResult1 = challengeMock.toStrings();
    Assert.assertEquals(expectedResult1[0], obtainedResult1[0]);
    Assert.assertEquals(expectedResult1[1], obtainedResult1[1]);
    Assert.assertEquals(expectedResult1[2], obtainedResult1[2]);
}

I get a NullPointerException due to “obtainedResult1 = challengeMock.toStrings();” that returns null.

I use PowerMock + Mockito running in Robolectric with rule(becouse its an Android project).

@Rule
public PowerMockRule rule = new PowerMockRule();

Where is the problem?

Answer 1

You don’t need PowerMock for this; a Mockito mock will be just fine. But normally, a mock has no functionality in its methods, which is why toStrings() isn’t returning the value that you expect. To change this, you need the CALLS_REAL_METHODS default answer.

So my recommendation would be to change the line where you create the mock (the third non-empty line of testToStrings) to something like this.

Challenge challengeMock = Mockito.mock(Challenge.class, Mockito.CALLS_REAL_METHODS );

I have tested this, and your test passes if you make this change.