Test Exception type using Mockito Junit

Question

Hi all I am completely new to spring-boot and Junit Mockito I am trying to check if my method is throwing a correct exception Below is the method from my service class

    public Optional<User> getUserByEmail(String emailaddress) {
    System.out.println("From DB");
    Optional<User> user = userDao.findByEmailAddress(emailaddress);
    user.orElseThrow(() -> new BadRequestException("User Not Found"));
    return user;
}

Below is my Test Method

    @Test
@DisplayName("TextCase to check if We are able to get Correct User")
public void getUserByEmailExceptionTest() {
    Mockito.when(userDao.findByEmailAddress("mokal006@gmail.com"))
    .thenThrow(UserNotFoundException.class);
     assertThrows(UserNotFoundException.class, () -> {
        LibraryUserDetailsService.getUserByEmail("mokal006@gmail.com");
    });
    
    
}

Now, this test is getting passed even if I am throwing the wrong exception in the actual method.

Can you provide more of your test setup? How are you injecting the Dao into the Service? Is this the onlyu expcetion you are mocking? — Pavel Polivka, Dec 16 '20 at 15:03
You never get to the orElseThrow part in your code because UserNotFounfException kicks in first and is handed through to the caller. Thus assertThrows catches it as expected. — johanneslink, Dec 17 '20 at 06:13
@VishalMokal Instead of throwing an exception you could return Optional.empty() from your mock of userDao. — johanneslink, Dec 20 '20 at 15:07

Govinda Sakhare · Answer 1 · 2020-12-20T07:43:30.000

To understand why your test case is passing for the wrong exception type, check how assertThrows works internally. AssertThrows.java

try {
    // execute lambda expression passed in assertThrows
} catch (Throwable var5) {
    if (expectedType.isInstance(var5)) {
        // if type matches returns the exception back
        return var5; 
    }
    // ..
    // Else throws different exception
    throw new AssertionFailedError(message, var5);
}

JUnit 5 checks type of exception calling Class.isIntance(..), Class.isInstance(..) will return true even if the exception thrown is of the parent types. In your case, it's highly likely that the thrown exception is of parent types.

you can fix it by asserting on Class.

Throwable throwable =  assertThrows(Throwable.class, () -> {
    LibraryUserDetailsService.getUserByEmail("mokal006@gmail.com");
});
assertEquals(UserNotFoundException.class, throwable.getClass());

or by using solutions from here JUnit 5: How to assert an exception is thrown?

[EDIT]

As pointed out by johanneslink in comments, user.orElseThrow will be never executed. userDao.findByEmailAddress(...) will throw UserNotFoundException as there is no catch block exception will be propagated back to the caller hence BadRequestException won't be thrown and test case will always pass.

Thank You @Govinda for your answer, I tried this but still, the test case is getting passed I think itis because of mockito. — Vishal Mokal, Dec 17 '20 at 05:01
@VishalMokal what is the parent type of UserNotFoundException? and what is the exact exception thrown in this case? — Govinda Sakhare, Dec 17 '20 at 10:32
The problem is `user.orElseThrow` will be never executed, check johanneslink's comment. — Govinda Sakhare, Dec 20 '20 at 07:44

Test Exception type using Mockito Junit

1 Answers1