Mockito 在使用 when 时抛出 NPE

Question

I am currently stuck on a problem using Mockito and I can't find a solution.

This is my method I want to test:

 @Override
public WeatherData getData(String wmoId, String location) {
    // Creates a specific csv mapper
    CsvSchema schema = factory.createEmptySchemaWithHeaderAndCommaSeperator();
    CsvMapper mapper = factory.createCsvMapper();
    MappingIterator<WeatherData> order = factory.createNullMappingIterator();
    try {

        order = mapper.readerFor(WeatherData.class).with(schema)
                .readValues(factory.createBufferedInputStream(factory.createWmoUrl(wmoId)));
        WeatherData current = order.readAll().get(2);
        current.setStationName(location);
        return current;
    } catch (Exception e) {

        return createErrorWeatherData(location);
    } finally {
        try {
            order.close();
        } catch (IOException e) {

        }
    }
}

And this is my current test class

@ExtendWith(MockitoExtension.class)
class WeatherDataServiceImplTest {

@InjectMocks
WeatherDataServiceImpl service;

@Mock
Factory factory;

@Mock
CsvSchema schema;

@Mock
CsvMapper mapper;

@Mock
BufferedInputStream stream;

@Mock
MappingIterator<Object> iterator;

@BeforeEach
public void setup() {
    MockitoAnnotations.initMocks(this);
}

@Test
void testGetDataWithInvalidStreamReturnsErrorObject() throws Exception {
    lenient().when(factory.createCsvMapper()).thenReturn(mapper);
    lenient().when(factory.createEmptySchemaWithHeaderAndCommaSeperator()).thenReturn(schema);
    lenient().when(factory.createNullMappingIterator()).thenReturn(null);
    when(mapper.readerFor(WeatherData.class).with(schema).readValues(stream)).thenReturn(iterator);
    WeatherData data = service.getData("id", "location");
    // assertEquals("location", data.getStationName());

}

}

Now the problem is that whatever I do I always receive a NullPointerException for the

when(mapper.readerFor(WeatherData.class).with(schema).readValues(stream)).thenReturn(iterator);

I am new to Mockito and testing so I hope you can help me here.

Thanks!

Answer 1

You need to enable deep stubbing for chained function calls to work,

Just replace,

@Mock
CsvMapper mapper;

with

@Mock(answer = RETURNS_DEEP_STUBS)
CsvMapper mapper;