Using Mockito, how do I intercept a callback object on a void method?

callback, jaas, java, mockito, unit-testing

Solution

For functions returning `void`, use doAnswer()

doAnswer(...).when(mockedObject).handle(any(Callback[].class));

And an `Answer` that performs the interception must go in as the parameter to `doAnswer`, e.g. as an anonymous class:

new Answer() {
  public Object answer(InvocationOnMock invocation) {
      Object[] args = invocation.getArguments();
      Mock mock = invocation.getMock();
      return null;
  }}

In this case `args` will be the array `Callback[]`!

Problem

I'm using mockito to test a legacy JAAS/LDAP login module. The `javax.security.auth.callback.CallbackHandler` interface defines the function: ``` void handle(javax.security.auth.callback.Callback[] callbacks) ``` I'm expecting `callbacks` to contain a `NameCallback`, which is the object that needs to be manipulated to pass the test. Is there a way to mock this effectively, or would I be better off with a stubbed implementation of `CallbackHandler`?

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