static void register(BeanDefinitionRegistry registry,
                       Set<Definition> definitions) {
    register(registry, SpockMockPostprocessor.class, definitions);
  }
Register the processor with a {@link BeanDefinitionRegistry}. Not required when
using the Spocks {@link spock.lang.Specification} as registration is automatic.

@param registry the bean definition registry
@param definitions the initial mock/spy definitions
spock-spring/src/main/java/org/spockframework/spring/mock/SpockMockPostprocessor.java