How to inject multiple mocks of the same interface

Question

The Java class (called ServiceCaller) I wish to test has this:

@Autowired @Qualifier(value="serviceA") SomeService serviceA;  @Autowired @Qualifier(value="serviceB") SomeService serviceB; 

(there's a doWork() method that will check a condition and call either A or B).

How do I inject a mock of each service into the appropriate variable?

My Junit has this:

@InjectMocks ServiceCaller classUnderTest = new ServiceCaller();  @Mock SomeService mockServiceA; @Mock SomeService mockServiceB; 

Yet when I run my tests to check that service A/B called under the correct condition, I get null pointers as the mock hasn't been injected.

Obviously its because of multiple dependencies on the same interface (SomeService). Is there a way to specify the qualifier when declaring the mock service? Or do I need to have setters for the dependencies and set the old fashioned way?

Answer 1

It should be enough to name your mocks serviceA and serviceB. From Mockito documentation:

Property setter injection; mocks will first be resolved by type, then, if there is several property of the same type, by the match of the property name and the mock name.

In your example:

@InjectMocks ServiceCaller classUnderTest;  @Mock SomeService serviceA; @Mock SomeService serviceB; 

Note that it is not necessary to manually create class instance when using @InjectMocks.

Nevertheless I personally prefer injecting dependencies using constructor. It makes it easier to inject mocks in tests (just call a constructor with your mocks - without reflections tools or @InjectMocks (which is useful, but hides some aspects)). In addition using TDD it is clearly visible what dependencies are needed for the tested class and also IDE can generate your constructor stubs.

Spring Framework completely supports constructor injection:

@Bean public class ServiceCaller {     private final SomeService serviceA;     private final SomeService serviceB;      @Autowired     public ServiceCaller(@Qualifier("serviceA") SomeService serviceA,                          @Qualifier("serviceB") SomeService serviceB) { ... }      ... } 

This code can be tested with:

@Mock SomeService serviceA; @Mock SomeService serviceB;  //in a setup or test method ServiceCaller classUnderTest = new ServiceCaller(serviceA, serviceB);