各位好，今天小编会向大家介绍一下通过lambda和mockito.answer提升单元测试编写效率的方法，如果你受够了各种复杂的依赖，如果你受够了写重复冗余的单测代码，如果你想解放双手，成就人生梦想，那么请往下看。
一、前提背景
大家在测试Spring RestTemplate的时候，为了规避上下文带来的影响且保证单元测试的效率与独立性，使用mock技术是常用的手法。但是实际项目中，如果要从RestTemplate转为其他框架的时候，就需要修改所有的单元测试代码，也就是说，目前的代码还是依赖于框架的，还是不够独立：
public class SpringCloudRefactoringTest { private static final Long EXISTING_VARIA = 1L; private static final Map<String, Long> GOOD_HTTP_PARAMS = Collections.singletonMap("id", EXISTING_VARIA); private static final Long NON_EXISTING_VARIA = 15123123L; private static final Map<String, Long> NON_EXISTING_HTTP_PARAMS = Collections.singletonMap("id", NON_EXISTING_VARIA); private static final Long OVER_VARIA = 99999999L; private static final Map<String, Long> BAD_HTTP_PARAMS = Collections.singletonMap("id", BAD_VARIA); private static final ResponseEntity<SpringCloudResponse> ERROR_RESPONSE = new ResponseEntity<>(new SpringCloudFactResponse("NoSuchQuoteException", "No quote with id=15123123."), HttpStatus.OK); private static final ResponseEntity<SpringCloudFactResponse> ITEM_RESPONSE = new ResponseEntity<>(new SpringCloudFactResponse("success", new SpringCloudFact(1L, "OK")), HttpStatus.OK); @Test public void serviceShouldReturnFact() { RestTemplate restTemplate = mock(RestTemplate.class); when(restTemplate.getForEntity(FACT_URL, SpringCloudFactResponse.class, GOOD_HTTP_PARAMS)) .thenReturn(ITEM_RESPONSE); SpringCloudService myServiceUnderTest = new SpringCloudService(restTemplate); SpringCloudFact springCloudFact = myServiceUnderTest.retrieveFact(EXISTING_VARIA); assertThat(springCloudFact, is(new SpringCloudFact(EXISTING_VARIA, "OK"))); } @Test public void serviceShouldReturnNothing() { RestTemplate restTemplate = mock(RestTemplate.class); when(restTemplate.getForEntity(FACT_URL, SpringCloudFactResponse.class, NON_EXISTING_HTTP_PARAMS)) .thenReturn(ERROR_RESPONSE); SpringCloudService myServiceUnderTest = new SpringCloudService(restTemplate); SpringCloudFact springCloudFact = myServiceUnderTest.retrieveFact(NON_EXISTING_VARIA); assertThat(springCloudFact, is(nullValue())); } @Test(expected = ResourceAccessException.class) public void serviceShouldPropagateException() { RestTemplate restTemplate = mock(RestTemplate.class); when(restTemplate.getForEntity(FACT_URL, SpringCloudFactResponse.class, BAD_HTTP_PARAMS)) .thenThrow(new ResourceAccessException("I/O error")); SpringCloudService myServiceUnderTest = new SpringCloudService(restTemplate); myServiceUnderTest.retrieveFact(BAD_VARIA); } } |
从上面可以看出，单测代码不仅对RestTemplate有了强依赖，且有很多重复的地方。
二、优化方案
经过阅读mockito的说明文档，发现mockito除了常用的thenReturn、thenThrow方法，还有一个thenAnswer方法。这个方法通过接收参数，实现一个通用的接口，而这个通用接口基本上可以返回任何想要的东西。
相比于常用的thenReturn、thenThrow方法（只返回固定的值），thenAnswer可以计算返回值，也就是说T answer(InvocationOnMockinvocation)throwsThrowable和Java 8新特性中的函数式接口 java.util.function.Function的功能基本相同 ，唯一不同可能也就是 throws了吧。有了个这个方法，我们就可以进一步优化代码了：
public class SpringCloudServiceStepOneTest { private static final Long EXISTING_VARIA = 1L; private static final Map<String, Long> GOOD_HTTP_PARAMS = Collections.singletonMap("id", EXISTING_VARIA); private static final Long NON_EXISTING_VARIA = 15123123L; private static final Map<String, Long> NON_EXISTING_HTTP_PARAMS = Collections.singletonMap("id", NON_EXISTING_VARIA); private static final Long BAD_VARIA = 99999999L; private static final Map<String, Long> BAD_HTTP_PARAMS = Collections.singletonMap("id", BAD_VARIA); private static final ResponseEntity<SpringCloudFactResponse> ERROR_RESPONSE = new ResponseEntity<>(new SpringCloudFactResponse("NoSuchQuoteException", "No quote with id=15123123."), HttpStatus.OK); private static final ResponseEntity<SpringCloudFactResponse> ITEM_RESPONSE = new ResponseEntity<>(new SpringCloudFactResponse("success", new SpringCloudFact(1L, "OK")), HttpStatus.OK); @Test public void serviceShouldReturnFact() { RestTemplate restTemplate = restEndpointShouldAnswer(GOOD_HTTP_PARAMS, (invocation) -> ITEM_RESPONSE); SpringCloudService myServiceUnderTest = new SpringCloudService(restTemplate); SpringCloudFact springCloudFact = myServiceUnderTest.retrieveFact(EXISTING_VARIA); assertThat(springCloudFact, is(new SpringCloudFact(EXISTING_VARIA, "OK"))); } @Test public void serviceShouldReturnNothing() { RestTemplate restTemplate = restEndpointShouldAnswer(NON_EXISTING_HTTP_PARAMS, (invocation -> ERROR_RESPONSE)); SpringCloudService myServiceUnderTest = new SpringCloudService(restTemplate); SpringCloudFact springCloudFact = myServiceUnderTest.retrieveFact(NON_EXISTING_VARIA); assertThat(springCloudFact, is(nullValue())); } @Test(expected = ResourceAccessException.class) public void serviceShouldPropagateException() { RestTemplate restTemplate = restEndpointShouldAnswer(BAD_HTTP_PARAMS, (invocation -> {throw new ResourceAccessException("I/O error");})); SpringCloudService myServiceUnderTest = new SpringCloudService(restTemplate); myServiceUnderTest.retrieveFact(BAD_VARIA); } private RestTemplate restEndpointShouldAnswer(Map<String, Long> httpParams, Answer<ResponseEntity<SpringCloudFactResponse>> response){ RestTemplate restTemplate = mock(RestTemplate.class); when(restTemplate.getForEntity(FACT_URL, SpringCloudFactResponse.class, httpParams)).thenAnswer(response); return restTemplate; } } |
优化点：
可以直接看到HTTP参数与响应的对照关系
可以绕过处理逻辑，不需要URL，HTTP方法这些依赖
可以将RestTemplate的mock提取成一个通用的方法，单测代码依赖度更低
问题：
代码不优美，每个单测中都有RestTemplate
三、进一步优化
通过 @Before解决上述问题：
public class SpringCloudServiceStepTwoTest { private static final Long EXISTING_VARIA = 1L; private static final Map<String, Long> GOOD_HTTP_PARAMS = Collections.singletonMap("id", EXISTING_VARIA); private static final Long NON_EXISTING_VARIA = 15123123L; private static final Map<String, Long> NON_EXISTING_HTTP_PARAMS = Collections.singletonMap("id", NON_EXISTING_VARIA); private static final Long BAD_VARIA = 99999999L; private static final Map<String, Long> BAD_HTTP_PARAMS = Collections.singletonMap("id", BAD_VARIA); private static final ResponseEntity<SpringCloudFactResponse> ERROR_RESPONSE = new ResponseEntity<>(new SpringCloudFactResponse("NoSuchQuoteException", "No quote with id=15123123."), HttpStatus.OK); private static final ResponseEntity<SpringCloudFactResponse> ITEM_RESPONSE = new ResponseEntity<>(new SpringCloudFactResponse("success", new SpringCloudFact(1L, "OK")), HttpStatus.OK); private RestTemplate restTemplate; private SpringCloudService myServiceUnderTest; @Before public void setUp(){ restTemplate = mock(RestTemplate.class); myServiceUnderTest = new SpringCloudService(restTemplate); } @Test public void serviceShouldReturnFact() { restEndpointShouldAnswer(GOOD_HTTP_PARAMS, (invocation) -> ITEM_RESPONSE); SpringCloudFact springCloudFact = myServiceUnderTest.retrieveFact(EXISTING_VARIA); assertThat(springCloudFact, is(new SpringCloudFact(EXISTING_VARIA, "OK"))); } @Test public void serviceShouldReturnNothing() { restEndpointShouldAnswer(NON_EXISTING_HTTP_PARAMS, (invocation -> ERROR_RESPONSE)); SpringCloudFact springCloudFact = myServiceUnderTest.retrieveFact(NON_EXISTING_VARIA); assertThat(springCloudFact, is(nullValue())); } @Test(expected = ResourceAccessException.class) public void serviceShouldPropagateException() { restEndpointShouldAnswer(BAD_HTTP_PARAMS, (invocation -> {throw new ResourceAccessException("I/O error");})); myServiceUnderTest.retrieveFact(BAD_VARIA); } private void restEndpointShouldAnswer(Map<String, Long> httpParams, Answer<ResponseEntity<SpringCloudFactResponse>> response){ when(restTemplate.getForEntity(FACT_URL, SpringCloudFactResponse.class, httpParams)).thenAnswer(response); } } |
四、总结
thenAnswer+lambda的方法虽然不是通用所有的case，但还是能解决大部分的单测依赖度高与代码重复较高的问题，根据说明文档，还有restEndpointShouldAnswer这个方法应该可以更进一步简化代码。无论采用什么方法，核心的思想就是AIR（Automatic, Independent, Repeatable）原则，保证了这个原则，才是高质量的单测代码。
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