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

Assert by exception message:

    try {
        MyAgent.getNameByNode("d");
    } catch (Exception e) {
        Assert.assertEquals("Failed to fetch data.", e.getMessage());
    }

Answer 2

Make the exception happen like this:

when(obj.someMethod()).thenThrow(new AnException());

Verify it has happened either by asserting that your test will throw such an exception:

@Test(expected = AnException.class)

Or by normal mock verification:

verify(obj).someMethod();

The latter option is required if your test is designed to prove intermediate code handles the exception (i.e. the exception won't be thrown from your test method).

Answer 3

Use Mockito's doThrow and then catch the desired exception to assert it was thrown later.

@Test
public void fooShouldThrowMyException() {
    // given
    val myClass = new MyClass();
    val arg = mock(MyArgument.class);
    doThrow(MyException.class).when(arg).argMethod(any());
    Exception exception = null;

    // when
    try {
        myClass.foo(arg);
    } catch (MyException t) {
        exception = t;
    }

    // then
    assertNotNull(exception);
}

Answer 4

BDD Style Solution (Updated to Java 8)

Mockito alone is not the best solution for handling exceptions, use Mockito with Catch-Exception

Mockito + Catch-Exception + AssertJ

given(otherServiceMock.bar()).willThrow(new MyException());

when(() -> myService.foo());

then(caughtException()).isInstanceOf(MyException.class);

Sample code

• Mockito + Catch-Exception + Assertj full sample

Dependencies

• eu.codearte.catch-exception:catch-exception:2.0
• org.assertj:assertj-core:3.12.2

Answer 5

Updated answer for 06/19/2015 (if you're using java 8)

Just use assertj

Using assertj-core-3.0.0 + Java 8 Lambdas

@Test
public void shouldThrowIllegalArgumentExceptionWhenPassingBadArg() {
assertThatThrownBy(() -> myService.sumTingWong("badArg"))
                                  .isInstanceOf(IllegalArgumentException.class);
}

Reference: http://blog.codeleak.pl/2015/04/junit-testing-exceptions-with-java-8.html

Answer 6

Or if your exception is thrown from the constructor of a class:

@Rule
public ExpectedException exception = ExpectedException.none();

@Test
public void myTest() {    

    exception.expect(MyException.class);
    CustomClass myClass= mock(CustomClass.class);
    doThrow(new MyException("constructor failed")).when(myClass);  

}