Constructor injection with mocked object which has to set mocked value in constructor - mockito

Question

I'm trying to mock a class FooB, which has another component FooA injected via constructor injection. My problem is, that in constructor FooB a value from injected component FooA has to be set. My problem I don't know the way how to mock FooA. Usually I would do something like in the commented out code in a #BeforeAll and mock the value with Mockito.when. But at this stage FooB is already initialized.
#ExtendWith(SpringExtension.class)
#ContextConfiguration(classes = { FooB.class })
class FooTest {
#MockBean
private FooA fooA;
#Autowired
private FooB fooB;
// #BeforeAll
// void initMocks() {
// when(fooA.getFoo()).thenReturn("foo");
// }
}
#Component
public class FooB {
private final String foo;
public FooB(final FooA fooA) {
this.foo = fooA.getFoo(); // <- how do I get the mocked value in here?
}
}
#Component
public class FooA {
private String foo;
public String getFoo() {
return foo;
}
public void setFoo(final String foo) {
this.foo = foo;
}
}

Answer 1

The below code could solve what you are trying to do (Edit : Added both a test case that uses #SrringBootTest and without it as well)
If not using SpringBoot
#ExtendWith(SpringExtension.class)
#ContextConfiguration(classes = {FooB.class, FooTest.TestConfig.class})
class FooTest {
#Autowired
private FooB fooB;
#TestConfiguration
public static class TestConfig {
#Bean
FooA getFooA(){
FooA fooA = Mockito.mock(FooA.class);
when(fooA.getFoo()).thenReturn("foo from test");
return fooA;
}
}
#Test
void testFooB() {
assertEquals("foo from test", fooB.getFoo());
}
}
If using SpringBoot
#SpringBootTest
class FooTest {
#Autowired
private FooB fooB;
#TestConfiguration
public static class TestConfig {
#MockBean
private FooA fooA;
#PostConstruct
void initMocks() {
when(fooA.getFoo()).thenReturn("foo from test");
}
}
#Test
void testFooB() {
assertEquals("foo from test", fooB.getFoo());
}
}