In this recipe, we will stub a void method that doesn't return a value. The trick with void methods is that Mockito assumes that they do nothing by default, so there is no need to explicitly stub them (although you may do it).
If you do not want your void method to execute logic, you need to perform the following steps:
- Do nothing: Mockito stubs the method for you so that it does nothing.
- Explicitly tell Mockito that the void method does nothing; for the BDD approach, call
BDDMockito.willNothing().given(mock).methodToStub(), or in the standard way, callMockito.doNothing().when(mock).methodToStub(). - Regardless of the chosen approach in the
given(...)orwhen(...)method, you have to provide the mock object (and not the method call in the case of methods that return values). - Remember that the last passed value during the stubbing will be returned for each stubbed method call. In other words, say that you stub the mock as follows (the
willThrowanswer will be described in more detail in the next recipe):willThrow(new Exception1()).willNothing().given(personSaver).savePerson(smith);
Then, regardless of the number of
personSaver.savePerson(...)method executions, first an exception will be thrown, and then you will always have no action taken (until it is stubbed again).
What Mockito does internally when you start stubbing using the methods starting with do...(...) or will...(...) is that the MockitoCore.doAnswer(...) method is executed with a proper answer, which, in the case of void methods that don't do anything, is the DoesNothing answer.
It's worth mentioning that as a result of the execution of the doAnswer(...) method, we have the Stubber interface returned, which has several fluent API methods (that return Stubber itself), for example, the following one:
Stubber doNothing();
It also provides us with a method that returns the stubbed object, the when method (BDDMockito delegates method execution to the when method as well).
<T> T when(T mock);
This is why you can profit from Mockito's fluent API, and when you call the when method, you have access to the mocked object's methods.
- Refer to the Mockito documentation on the
doReturn()|doThrow()|doAnswer()|doNothing()|doCallRealMethod()family of methods from http://docs.mockito.googlecode.com/hg/1.9.5/org/mockito/Mockito.html#12