How do you verify that a method was never called on a null object?

Question

I have an Object that may be null.

I want to verify that when an object is null, it's method is not invoked.

I wrote a test case that looks like this:

    String str = mock(String.class);
    str = null;
    verify(str, never()).length();

But Mockito replies with:

org.mockito.exceptions.base.MockitoException: 
Cannot mock/spy class java.lang.String
Mockito cannot mock/spy following:
  - final classes
  - anonymous classes
  - primitive types

How do I verify that my a method is not invoked on a null Object?

On the contrary, I want to verify that *NO* methods are invoked on the nulled Object. — Some Noob Student, Nov 23 '13 at 00:30
I guess this is what you are looking for http://stackoverflow.com/questions/271526/avoiding-null-statements-in-java — Prateek, Nov 23 '13 at 00:31
What for? If a method is called on a null reference you'll get a NullPointerException and the test will fail as well. — Egor, Nov 23 '13 at 00:31
Making sure that you don't write code with null pointer exceptions in it isn't really what Mockito does. — Dawood ibn Kareem, Nov 23 '13 at 00:33

score 2 · Answer 1 · answered Nov 23 '13 at 18:39

You can't use mock operations on a null object reference.

But if any method is called on your null object reference, then you'll get a NPE - this should fail your test (unless you were expecting a NPE, of course).

You can also use assertNull() to be sure that str is in fact null, if this is part of your test result.

How do you verify that a method was never called on a null object?

1 Answers1