SomeManagedBean.java

public class SomeManagedBean {
  private ServiceA someService;
  
  public int doSomething() {
    ... logic to be tested ...
    someService.doSomethingElse();
  }

  public void setSomeService(ServiceA someService) {
    this.someService = someService;
  }
}


}

SomeManagedBeanTest.java

public class SomeManagedBeanTest {
  @Test
  public void doSomethingTest() {
    SomeManagedBean testMe = new SomeManagedBean();
    testMe.setSomeService(new MockServiceA());
    int actualResult = testMe.doSomething();
    assertEquals(1, actualResult);
  }