Java Unit Tests giving NullPointer Exception

Question

i have a unit test throwing NullPointer Exception when i put the test in another file, its running fine below is the piece of code. other tests in the same file are running without any errors.

@Test
public void validateShouldFailIfThereExistsABillingCycleWithSameId() {
 final String expectedErrorMessage = "Billing Cycle with id " + id + " already exists";
 when(billingCycleServiceAuditable.
 findBillingCycleById(id, locale, DefaultAuth.SYSTEM_USER_NAME.getValue())).
 thenReturn(Optional.of(billingCycle));
 when(messageService.getMessage(I18Code.MESSAGE_CHARGING_BILLING_CYCLE_EXISTS.getCode(),
 new String[]{id.toString()}, locale)).thenReturn(expectedErrorMessage);
 when(mapper.map(billingCycle)).thenReturn(billingCycleDto);
 when(mapper.map(billingCycleDto)).thenReturn(billingCycle);
 final CommonResponse response = billingCycleValidator.validate(billingCycle, userAction, locale, DefaultAuth.SYSTEM_USER_NAME.getValue());
 assertNotNull(response);
 assertEq @Test
public void validateShouldFailIfThereExistsABillingCycleWithSameId() {
 final String expectedErrorMessage = "Billing Cycle with id " + id + " already exists";
 when(billingCycleServiceAuditable.
 findBillingCycleById(id, locale, DefaultAuth.SYSTEM_USER_NAME.getValue())).
 thenReturn(Optional.of(billingCycle));
 when(messageService.getMessage(I18Code.MESSAGE_CHARGING_BILLING_CYCLE_EXISTS.getCode(),
 new String[]{id.toString()}, locale)).thenReturn(expectedErrorMessage);
 when(mapper.map(billingCycle)).thenReturn(billingCycleDto);
 when(mapper.map(billingCycleDto)).thenReturn(billingCycle);
 final CommonResponse response = billingCycleValidator.validate(billingCycle, userAction, locale, DefaultAuth.SYSTEM_USER_NAME.getValue());
 assertNotNull(response);
 assertEquals(expectedErrorMessage, response.getNarrative());
 verify(billingCycleServiceAuditable,
 times(1))
 .findBillingCycleById(anyLong(), any(Locale.class), anyString());
}uals(expectedErrorMessage, response.getNarrative());
 verify(billingCycleServiceAuditable,
 times(1))
 .findBillingCycleById(anyLong(), any(Locale.class), anyString());
}

• Maciej Kowalski: include the stacktrace

Answer 1

At the beginning of your test class make sure the class is annotated with testrunner as bellow

@RunWith(MockitoJUnitRunner.class)
public class BillingCycleValidatorImplCreateBillingCycleActionTest {
}