Testing spring bean with post construct

If you want to write a unit test of A, then don't use Spring. Instead, instantiate A yourself and pass a stub/mock of B (either by using constructor injection or ReflectionTestUtils to set the private field).

For example:

@Service
public class A {

    private final B b;    

    @Autowired
    public A(B b) {
        this.b = b;
    }

    @PostConstruct
    public void setup() {
       b.call(param);
    }
}

-

public class Test {

    @Test
    public void test() throws Exception {
        B b = mock(b);
        A a = new A(b);
        // write some tests for A
    }

}

If you have to use Spring, because you want to write an integration test, use a different application context, where you replace B with a stub/mock.

For example, assuming B is instantiated in a Production class like this:

@Configuration
public class Production {

    @Bean
    public B b() {
        return new B();
    }

}

Write another @Configuration class for your tests:

@Configuration
public class Tests {

    @Bean
    public B b() {
        // using Mockito is just an example
        B b = Mockito.mock(B.class); 
        Mockito.when(b).thenReturn("smth"); 
        return b;
    }

}

Reference it in your test with the @SpringApplicationConfiguration annotation:

@SpringApplicationConfiguration(classes = { Application.class, Tests.class })

Just had this exact problem on a project I'm working on, Here is the solution I used in terms of the question code:

1. @Autowire in the bean with the @PostConstruct to your test.
2. Do your setup in the @Before.
3. Explicitly call the @PostConstruct at the end of your @Before.

@RunWith(SpringJUnit4ClassRunner.class)
@SpringApplicationConfiguration(classes = { Application.class, Config.class })
@WebIntegrationTest(randomPort = true)
public class Test {

    // wire in the dependency as well
    @Autowired
    A a;

    @Autowired
    B b;

    @Before
    public void setUp() throws Exception {
        when(b.call(any())).thenReturn("smth");
        
        // "manual" call to @PostConstruct which will now work as expected
        a.setup(); 
    }

    @Test
    public void test() throws Exception {
        // test...
    }
}

Obviously your @PostConstruct method has to be idempotent as its going to get called twice. Also it assumes default singleton bean behaviour.