如何为Spring Boot Service的updateCar方法实现单元测试全覆盖

问题背景 #

我正在为Spring Boot Service编写单元测试，希望实现updateCar方法的全覆盖。

目标方法（updateCar） #

public void updateCar(String id, String carModel, Integer HP, Integer year, String designer) {
    Garage garage = garageRepository.findById(id)
            .orElseThrow(() -> new IllegalStateException(
                    "A car with the id " + id + " is not in our Garage."));
    if(carModel != null && carModel.length() > 0 && !Objects.equals(garage.getCarModel(), carModel)) {
        garage.setCarModel(carModel);
    }
    if(HP != null && !Objects.equals(garage.getHP(), HP)) {
        garage.setHP(HP);
    }
    if(year != null && !Objects.equals(garage.getYear(), year)) {
        garage.setYear(year);
    }
    if(designer != null && designer.length() > 0 && !Objects.equals(garage.getDesigner(), designer)) {
        garage.setDesigner(designer);
    }
    garageRepository.save(garage);
}

当前测试代码 #

@Test
@DisplayName("Update Car Test")
void testUpdateCar() {

    Garage updatedGarage = new Garage();
    String id = "630ca281f12905d5f5249f08";
    String carModel = "Updated carModel";
    int HP = 480;
    int year = 1964;
    String designer = "Updated designer";

    updatedGarage.setId(id);
    updatedGarage.setCarModel(carModel);
    updatedGarage.setHP(HP);
    updatedGarage.setYear(year);
    updatedGarage.setDesigner(designer);

    when(garageRepository.findById(id))
            .thenReturn(Optional.of(updatedGarage));
    garageService.updateCar(id, carModel, HP, year, designer);

    when(garageRepository.save(updatedGarage))
            .thenReturn(updatedGarage);
    verify(garageRepository).findById(id);
}

当前问题 #

当前测试仅获得部分覆盖率，未覆盖updateCar方法中的garage.setCarModel(carModel)、garage.setHP(HP)、garage.setYear(year)以及garage.setDesigner(designer)逻辑，请问如何实现该方法的测试全覆盖？

全覆盖测试方案 #

要覆盖所有分支逻辑，需要针对每个字段的更新条件、不更新条件，以及findById返回空的异常场景分别编写测试用例。

1. 覆盖字段更新的核心场景 #

当前测试中传入的参数和模拟的Garage对象原有值完全一致，导致if条件不成立，自然不会执行set方法。需要让传入的参数和原有值不同：

@Test
@DisplayName("Update all fields successfully when values are different")
void testUpdateAllFields() {
    // 初始化原有车库对象，设置初始值
    String id = "630ca281f12905d5f5249f08";
    Garage existingGarage = new Garage();
    existingGarage.setId(id);
    existingGarage.setCarModel("Original Model");
    existingGarage.setHP(300);
    existingGarage.setYear(1960);
    existingGarage.setDesigner("Original Designer");

    // 模拟Repository返回原有对象
    when(garageRepository.findById(id)).thenReturn(Optional.of(existingGarage));

    // 传入不同的更新参数
    String newModel = "Updated carModel";
    Integer newHP = 480;
    Integer newYear = 1964;
    String newDesigner = "Updated designer";

    garageService.updateCar(id, newModel, newHP, newYear, newDesigner);

    // 验证每个字段都被正确更新
    assertEquals(newModel, existingGarage.getCarModel());
    assertEquals(newHP, existingGarage.getHP());
    assertEquals(newYear, existingGarage.getYear());
    assertEquals(newDesigner, existingGarage.getDesigner());

    // 验证save方法被调用
    verify(garageRepository).save(existingGarage);
}

2. 覆盖字段不更新的分支场景 #

针对每个字段的if条件不成立的情况（参数为空、空字符串、与原有值相同），分别编写测试：

针对carModel的不更新测试

@Test
@DisplayName("Do not update carModel when new value matches original")
void testNotUpdateCarModelWhenSame() {
    String id = "630ca281f12905d5f5249f08";
    Garage existingGarage = new Garage();
    existingGarage.setId(id);
    String originalModel = "Original Model";
    existingGarage.setCarModel(originalModel);

    when(garageRepository.findById(id)).thenReturn(Optional.of(existingGarage));

    // 传入和原有值相同的carModel
    garageService.updateCar(id, originalModel, null, null, null);

    // 验证carModel未被修改
    assertEquals(originalModel, existingGarage.getCarModel());
    verify(garageRepository).save(existingGarage);
}

@Test
@DisplayName("Do not update carModel when new value is empty string")
void testNotUpdateCarModelWhenEmpty() {
    String id = "630ca281f12905d5f5249f08";
    Garage existingGarage = new Garage();
    existingGarage.setId(id);
    existingGarage.setCarModel("Original Model");

    when(garageRepository.findById(id)).thenReturn(Optional.of(existingGarage));

    // 传入空字符串
    garageService.updateCar(id, "", null, null, null);

    assertEquals("Original Model", existingGarage.getCarModel());
    verify(garageRepository).save(existingGarage);
}

针对HP的不更新测试

@Test
@DisplayName("Do not update HP when new value matches original")
void testNotUpdateHPWhenSame() {
    String id = "630ca281f12905d5f5249f08";
    Garage existingGarage = new Garage();
    existingGarage.setId(id);
    Integer originalHP = 300;
    existingGarage.setHP(originalHP);

    when(garageRepository.findById(id)).thenReturn(Optional.of(existingGarage));

    garageService.updateCar(id, null, originalHP, null, null);

    assertEquals(originalHP, existingGarage.getHP());
    verify(garageRepository).save(existingGarage);
}

@Test
@DisplayName("Do not update HP when new value is null")
void testNotUpdateHPWhenNull() {
    String id = "630ca281f12905d5f5249f08";
    Garage existingGarage = new Garage();
    existingGarage.setId(id);
    existingGarage.setHP(300);

    when(garageRepository.findById(id)).thenReturn(Optional.of(existingGarage));

    garageService.updateCar(id, null, null, null, null);

    assertEquals(300, existingGarage.getHP());
    verify(garageRepository).save(existingGarage);
}

同理，为year和designer编写上述类似的不更新场景测试即可覆盖对应分支。

3. 覆盖找不到车辆的异常场景 #

@Test
@DisplayName("Throw exception when car not found by id")
void testUpdateCarNotFound() {
    String id = "non-existent-id";
    when(garageRepository.findById(id)).thenReturn(Optional.empty());

    // 验证抛出指定异常
    IllegalStateException exception = assertThrows(IllegalStateException.class, () -> {
        garageService.updateCar(id, "New Model", 500, 2020, "New Designer");
    });

    assertEquals("A car with the id " + id + " is not in our Garage.", exception.getMessage());
    // 验证save方法未被调用
    verify(garageRepository, never()).save(any(Garage.class));
}

4. 混合场景测试（部分字段更新） #

测试部分字段更新、部分不更新的情况，确保逻辑兼容：

@Test
@DisplayName("Update only partial fields")
void testUpdatePartialFields() {
    String id = "630ca281f12905d5f5249f08";
    Garage existingGarage = new Garage();
    existingGarage.setId(id);
    existingGarage.setCarModel("Original Model");
    existingGarage.setHP(300);
    existingGarage.setYear(1960);
    existingGarage.setDesigner("Original Designer");

    when(garageRepository.findById(id)).thenReturn(Optional.of(existingGarage));

    // 只更新HP和year，其他参数保持原有值或为空
    Integer newHP = 480;
    Integer newYear = 1964;
    garageService.updateCar(id, "Original Model", newHP, newYear, "");

    // 验证HP和year被更新，其他字段不变
    assertEquals("Original Model", existingGarage.getCarModel());
    assertEquals(newHP, existingGarage.getHP());
    assertEquals(newYear, existingGarage.getYear());
    assertEquals("Original Designer", existingGarage.getDesigner());

    verify(garageRepository).save(existingGarage);
}

内容的提问来源于stack exchange，提问作者WorkWork