Friday, March 19, 2010

Mockito's @InjectMocks annotation does reflection-based DI

I've been using @InjectMocks heavily lately since it came out in version 1.8.3 of mockito. The javadocs for this annotation state that it uses setter injection to inject its dependencies. Being a lazy developer, I was writing a unit test yesterday at work and forgot to write the setter methods for a couple of dependencies on the SUT that I was testing. Lo and behold, the test passed and all mock verifications were satisfied. Very confused, I went back to some other unit tests and their SUTs and removed the setter methods. In all of my cases, the tests continued to pass. A quick note to the mockito list confirms what I discovered--@InjectMocks actually is using a reflection-based DI scheme, not unlike what Spring does when you annotate collaborator fields in a Spring bean with @Autowired and @Resource. Very cool feature, as this further reduces code noise. Here is the discussion on Google Groups.