Custom Answers and Callbacks

Sometimes, simply returning a fixed value with when().thenReturn() isn't enough for your mock objects.

• What if a mock method needs to modify an argument passed to it?
• What if it needs to execute a callback function?
• What if its return value depends on multiple inputs in a complex, dynamic way?

These advanced scenarios call for custom logic within your mocks.

Mockito provides the org.mockito.stubbing.Answer interface. This powerful tool lets you define custom behavior for a mocked method call.

• Think of it as writing a small piece of code that runs whenever the mocked method is invoked.
• The Answer interface has a single method: Object answer(Invocation invocation) throws Throwable;.

It gives you fine-grained control over mock responses.