Nullpointer Exception for mocking final method

Question

Getting NullPointerException when trying to mock Aggregations.getAsMap()

I have already tried other different ways by using PowerMockito.doReturn(map).when(aggs).getAsMap() but still facing same issue

@PrepareForTest(Aggregations.class)
public class TestExample extends PowerMockTestCase {

    @Test
    public void testMyMethod() {
        Aggregations aggs = PowerMockito.mock(Aggregations.class);
        Cardinality cardinality = Mockito.mock(Cardinality.class);
        Map<String, Aggregation> map = new HashMap<String, Aggregation>();
        map.put("sample", cardinality);
        Mockito.when(aggs.getAsMap()).thenReturn(map);
    }

}

Mockito.when(aggs.getAsMap()).thenReturn(map);

while debugging aggs value is containing below value

{Aggregations$MockitoMock$485838759@3084} Method threw 'java.lang.NullPointerException' exception. Cannot evaluate org.elasticsearch.search.aggregations.Aggregations$MockitoMock$485838759.toString()

Using testng and below version of jars

powermock-api-mockito-2.0.2.jar

mockito-core-2.23.0.jar

Answer 1

The NullPointerException comes from the invocation of the getAsMap method.

Using Mockito.doReturn(map).when(aggs).getAsMap(); instead should solve that issue.

However there seems to be a bug in PowerMockito as writing it like this is not supposed to trigger the invocation of the getAsMap() method (which still happens).

I suggest you create a bug ticket in their bugtracker for this issue.

---

If you enable final mocking for Mockito (see here) running the test is successful.

@RunWith(MockitoJUnitRunner.class)
public class TestExample {

    @Test
    public void testMyMethod() {
        Aggregations aggs = Mockito.mock(Aggregations.class);
        Cardinality cardinality = Mockito.mock(Cardinality.class);
        Map<String, Aggregation> map = new HashMap<String, Aggregation>();
        map.put("sample", cardinality);

        Mockito.doReturn(map).when(aggs).getAsMap();
        Assert.assertEquals(map, aggs.getAsMap());
    }
}

---

Another option might be to work with a real Aggregations object instead:

@Test
public void testMyMethod() {

    Cardinality cardinality = Mockito.mock(Cardinality.class);
    Mockito.when(cardinality.getName()).thenReturn("sample");

    List<Aggregation> list = new ArrayList<>();
    list.add(cardinality);

    Aggregations aggs = new Aggregations(list);
    Map<String, Aggregation> map = aggs.getAsMap();

    Assert.assertEquals(1, map.size());
    Assert.assertEquals(cardinality, map.get("sample"));
}