Test-Driven Java Development, Second Edition - Second Edition

Mock objects

Mock objects simulate the behavior of real (often complex) objects. They allow us to create an object that will replace the real one used in the implementation code. A mocked object will expect a defined method with defined arguments to return the expected result. It knows in advance what is supposed to happen and how we expect it to react.

Let's take a look at one simple example:

TicTacToeCollection collection = mock(TicTacToeCollection.class); 
assertThat(collection.drop()).isFalse();doReturn(true).when(collection).drop(); 

assertThat(collection.drop()).isTrue();

First, we defined collection to be a mock of TicTacToeCollection. At this moment, all methods from this mocked object are fake and, in the case of Mockito, return default ...