When we write tests or specifications using Spock for our Spring Boot application, we might want to replace some Spring components with a stub or mock version. With the stub or mock version we can write expected outcomes and behaviour in our specifications. Since Spock 1.2 and the Spock Spring extension we can use the @SpringBean annotation to replace a Spring component with a stub or mock version. (This is quite similar as the @MockBean for Mockito mocks that is supported by Spring Boot). We only have to declare a variable in our specification of the type of the Spring component we want to replace. We directly use the Stub() or Mock() methods to create the stub or mock version when we define the variable. From now on we can describe expected output values or behaviour just like any Spock stub or mock implementation.