使用Mock运行单元测试报错：when()参数需为Mock对象方法调用

问题根源 #

你用@Mock注解声明了apiClientUtilsMock作为Mock对象，但在setup()方法里又执行了apiClientUtilsMock = new ApiClientUtils(new ApiClientTimeoutConfiguration());——这行代码直接把Mockito生成的Mock对象覆盖成了真实的ApiClientUtils实例。后续调用when(apiClientUtilsMock.createClientCredentialsResourceDetails(...))时，操作的是真实对象而非Mock对象，因此触发报错。

修复步骤 #

直接删除setup()方法中创建真实ApiClientUtils实例的代码行：

apiClientUtilsMock = new ApiClientUtils(new ApiClientTimeoutConfiguration());

Mockito会通过@Mock注解自动生成并注入Mock实例，无需手动创建真实对象。

修复后的完整测试类代码 #

@ExtendWith(MockitoExtension.class)
class CustomerDaoConfigurationTest {

    private CustomerDaoConfiguration customerDaoConfiguration;

    private CustomerApiProperties properties;
    @Mock
    private ApiClientUtils apiClientUtilsMock;
    @Mock // 单元测试无需@MockBean，换成@Mock即可
    private ApiClientTimeoutConfiguration apiClientTimeoutConfiguration;


    @BeforeEach
    void setup() {
        properties = new CustomerApiProperties();
        properties.setBaseUrl("MockBaseUrl");
        properties.setOauth(new OAuthProperties("token-url", "client-id", "client-secret"));

        customerDaoConfiguration = new CustomerDaoConfiguration(properties, apiClientUtilsMock, apiClientTimeoutConfiguration);

    }

    @Test
    void shouldCreateValidRestTemplateWhenPropertiesAreProvided() {

        ClientCredentialsResourceDetails clientCredentialsResourceDetails = new ClientCredentialsResourceDetails();
        clientCredentialsResourceDetails.setClientSecret("client-secret");
        clientCredentialsResourceDetails.setClientId("client-id");
        clientCredentialsResourceDetails.setTokenName("token-name");
        clientCredentialsResourceDetails.setAccessTokenUri("token-url");

        OAuthProperties oauth = properties.getOauth();

        List<HttpMessageConverter<?>> messageConverters = new ArrayList<>();
        messageConverters.add(new JsonApiHttpMessageConverter(new ResourceConverter(), new ObjectMapper()));

        when(apiClientUtilsMock.createClientCredentialsResourceDetails(oauth)).thenReturn(clientCredentialsResourceDetails);

        RestTemplate createdRestTemplate = customerDaoConfiguration.customerRestTemplate(new SimpleClientHttpRequestFactory(), messageConverters);

        assertThat(createdRestTemplate.getMessageConverters().size(), is(1));
        HttpMessageConverter<?> messageConverter = createdRestTemplate.getMessageConverters().get(0);
        assertThat(messageConverter, is(instanceOf(JsonApiHttpMessageConverter.class)));

    }
}

额外说明 #

• @MockBean是Spring Boot集成测试专用注解，用于向Spring容器注入Mock对象；纯单元测试场景下，用@Mock配合MockitoExtension即可完成Mock对象的创建。
• 这是Mockito使用的常见坑点：如果用注解声明了Mock对象，切勿再手动创建真实实例覆盖它，否则Mockito无法拦截方法调用进行Mock配置。

内容的提问来源于stack exchange，提问作者ljs