Throw a RuntimeException when invoking an unstubbed method

You can set a default answer for a mock. All methods that aren't stubbed will use this default answer.

public void testUnstubbedException() {
    // Create a mock with all methods throwing a RuntimeException by default
    SomeClass someClass = mock( SomeClass .class, new RuntimeExceptionAnswer() );

    doReturn(1).when(someClass).getId(); // Must use doReturn

    int id = someClass.getId(); // Will return 1

    someClass.unstubbedMethod(); // Will throw RuntimeException
}

public static class RuntimeExceptionAnswer implements Answer<Object> {

    public Object answer( InvocationOnMock invocation ) throws Throwable {
        throw new RuntimeException ( invocation.getMethod().getName() + " is not stubbed" );
    }

}

Note that you cannot use when with this functionality, since the method is called before when (How does mockito when() invocation work?) and it will throw a RuntimeException before the mock goes into stubbing mode.

Therefore, you must use doReturn for this to work.

The best way to do this is with the verifyNoMoreInteractions and ignoreStubs static methods. Call these after the "act" part of your test; and you'll get a failure if any unstubbed methods were called but not verified.

verifyNoMoreInteractions(ignoreStubs(myMock));

This is described at https://static.javadoc.io/org.mockito/mockito-core/2.8.47/org/mockito/Mockito.html#ignore_stubs_verification although I believe that the code example there currently contains a misprint.