Question

I’d like to use strict mocks, at least when developing for the first time some tests against old code, so any methods invoked on my mock will throw an exception if I didn’t specifically define expectations.

From what I’ve come to see, Mockito if I didn’t define any expectations will just return null, which will later on cause a NullPointerException in some other place.

Is it possible to do that? If yes, how?

Answer 1

What do you want it to do?

You can set it to RETURN_SMART_NULLS, which avoids the NPE and includes some useful info.

You could replace this with a custom implementation, for example, that throws an exception from its answer method:

@Test
public void test() {
    Object mock = Mockito.mock(Object.class, new NullPointerExceptionAnswer());
    String s = mock.toString(); // Breaks here, as intended.
    assertEquals("", s);
}

class NullPointerExceptionAnswer<T> implements Answer<T> {
    @Override
    public T answer(InvocationOnMock invocation) throws Throwable {
        throw new NullPointerException();
    }
}