SpringBootTest - classes - Mock a required constructor argument

Question

We are using SpringBootTest for Integration testing.

Let us say for example that we have a class : ClassWithManyConstructorArgs with one Required Constructor Argument (another class, DependencyA) and no default constructor.

Example : public ClassWithManyConstructorArgs(DependencyA a){ }

Our Integration test is configured as :

@SpringBootTest ( classes = [ClassWithManyConstructorArgs::class] )

I need to provide mocked implementations of the DependencyA class. How can I do that? What is the syntax to tell the system to initialize the ClassWithManyConstructorArgs using mocked DependencyA object?

Answer 1

Assume we have two beans: ServiceA and ServiceB.

ServiceA depends on ServiceB. for testing,

1. we load ServiceA into our test applicationContext(@SpringBootTest(classes = {ServiceA.class})).
2. use @Autowired on ServiceA for injecting the real instance that need to be tested, use @MockBean on ServiceB for creating a mocked bean that need to support the testing.
3. now we can test our methods in ServiceA with the mocked bean serviceB.

here's the code:

@SpringBootTest(classes = {ServiceA.class})
public class ServiceATest {
  @MockBean
  private ServiceB serviceB;

  @Autowired
  private ServiceA serviceA;

  @Test
  void testMethodA() {
    serviceA.methodA();
  }
}