Mockito How to mock and assert a thrown exception?

Question

I\'m using mockito in a junit test. How do you make an exception happen and then assert that it has (generic pseudo-code)

Answer 1

Using mockito, you can make the exception happen.

when(testingClassObj.testSomeMethod).thenThrow(new CustomException());

Using Junit5, you can assert exception, asserts whether that exception is thrown when testing method is invoked.

@Test
@DisplayName("Test assert exception")
void testCustomException(TestInfo testInfo) {
    final ExpectCustomException expectEx = new ExpectCustomException();

     InvalidParameterCountException exception = assertThrows(InvalidParameterCountException.class, () -> {
            expectEx.constructErrorMessage("sample ","error");
        });
    assertEquals("Invalid parametercount: expected=3, passed=2", exception.getMessage());
}

Find a sample here: assert exception junit