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Stubbing return values covers the happy path, but real code must also handle errors and changing state. Mockito lets you stub mocks to throw exceptions and to vary their answers per call.

Use thenThrow to make a stubbed method raise an exception, so you can test your error handling.

Combine the throwing stub with assertThrows to verify your code reacts correctly.

For void methods you cannot use when(...) directly. Use doThrow(...).when(mock).method() instead.

Pass multiple arguments to thenReturn to return different values on successive calls. The last value repeats once exhausted.

You can also chain calls. Each call describes the next invocation in order.

A common pattern: succeed a few times, then fail. This models flaky resources like a retrying network client.

A mock can only throw a checked exception that the stubbed method declares. Throwing an undeclared checked exception causes a runtime error from Mockito.

The do* family also supports chaining and is required when stubbing spies or void methods.

Exception and consecutive stubbing let you exercise retry logic, fallback paths, and stateful sequences without building complex fake objects.

You can now drive a mock through a full sequence of success and failure to validate resilient code.

How do you make a stubbed method return 1, then 2 on its second call?

You learned advanced stubbing:

• thenThrow / doThrow simulate errors
• Multiple thenReturn args or chains give consecutive values
• Mocks can only throw declared checked exceptions
• Use do* for void methods and spies