Mokito 관련 질문

@Test
void openStudy() {
    // Given
    StudyService studyService = new StudyService(memberService, studyRepository);
    Study study = new Study(10, "더 자바, 테스트");
    assertNull(study.getOpenedDateTime());
    given(studyRepository.save(study)).willReturn(study);

    // When
    studyService.openStudy(study);

    // Then
    assertEquals(StudyStatus.OPENED, study.getStatus());
    assertNotNull(study.getOpenedDateTime());
    then(memberService).should().notify(study);
}

@Mock MemberService memberService;

와 같이 Mock 주입한 StudyService를 사용하지 않고 

StudyService studyService = new StudyService(memberService, studyRepository);

와 같이 StudyService 를 직접 생성해주는 이유는 무엇인가요?