title: Unit testing Rest client with ClientHttpRequestInterceptor
body: <p>The below unit test fails.  I am printing the requests and responses and can confirm that MockRestServiceServer returns the mocked JSON when the endpoint is invoked.  When I change the test to talk directly to the server the unit test passes.  Not sure what I'm doing wrong</p>
  
  <pre><code>@RunWith(SpringJUnit4ClassRunner.class)
  @WebAppConfiguration
  @ContextConfiguration(classes = {Application.class, Beans.class})
  public class BillingSystemClientImplTest {
  
      private MockRestServiceServer mockServer;
  
      @Autowired
      private RestTemplate restTemplate;
  
      @Autowired
      private Properties properties;
  
      @Autowired
      private BillingSystemClient client;
  
      @Before
      public void setUp() {
          mockServer = MockRestServiceServer.createServer(restTemplate);
      }
  
      @Test
      public void testGetAccount() throws Exception {
  
          Resource resource = new ClassPathResource("/account.json", getClass());
  
          UriComponents uri = UriComponentsBuilder.fromUriString(properties.getAccountResource())
                  .buildAndExpand("53737803");
  
          mockServer.expect(requestTo(uri.toUriString()))
                  .andExpect(method(HttpMethod.GET))
                  .andRespond(withSuccess(resource, MediaType.APPLICATION_JSON));
  
          AccountResponse response = client.getAccount("53737803");
  
          Assert.assertNotNull(response.getAccountNumber());
  
          mockServer.verify();
  
      }
  
  }
  </code></pre>
  
  <p>The exception below complains that the response object is null.  This object is mapped from the response</p>
  
  <pre><code>    response = restTemplate.getForObject(uriComponents.toUri(), AccountResponse.class);
  </code></pre>
  
  <p>And the exception</p>
  
  <pre><code>java.lang.NullPointerException
      at com.something.ws.client.BillingSystemClientImplTest.testGetAccount(BillingSystemClientImplTest.java:74)
      at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
      at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
      at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
      at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
      at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
      at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
      at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
      at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)
      at org.springframework.test.context.junit4.statements.RunBeforeTestMethodCallbacks.evaluate(RunBeforeTestMethodCallbacks.java:75)
      at org.springframework.test.context.junit4.statements.RunAfterTestMethodCallbacks.evaluate(RunAfterTestMethodCallbacks.java:86)
      at org.springframework.test.context.junit4.statements.SpringRepeat.evaluate(SpringRepeat.java:84)
      at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
      at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:254)
      at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:89)
      at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
      at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
      at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
      at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
      at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
      at org.springframework.test.context.junit4.statements.RunBeforeTestClassCallbacks.evaluate(RunBeforeTestClassCallbacks.java:61)
      at org.springframework.test.context.junit4.statements.RunAfterTestClassCallbacks.evaluate(RunAfterTestClassCallbacks.java:70)
      at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
      at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.run(SpringJUnit4ClassRunner.java:193)
  </code></pre>
  
  <p>Turns out this is happening because of how I setup my restTemplate</p>
  
  <pre><code>SimpleClientHttpRequestFactory requestFactory = new SimpleClientHttpRequestFactory();
          BufferingClientHttpRequestFactory bufferingClientHttpRequestFactory = new BufferingClientHttpRequestFactory(requestFactory);
          requestFactory.setOutputStreaming(false);
  
          RestTemplate restTemplate = new RestTemplate();
          restTemplate.getInterceptors().add(mpxLoggingRequestInterceptor());
          restTemplate.setErrorHandler(mpxErrorHandler());
          restTemplate.getMessageConverters().add(new StringHttpMessageConverter());
          restTemplate.getMessageConverters().add(new MappingJackson2HttpMessageConverter());
          restTemplate.setRequestFactory(new BufferingClientHttpRequestFactory(new SimpleClientHttpRequestFactory()));
          restTemplate.getInterceptors().add(new GenericRequestInterceptor());
          restTemplate.setRequestFactory(bufferingClientHttpRequestFactory);
  </code></pre>
  
  <p>If I remove the RequestFactory and Interceptor the tests would pass. This is an issue with the unit tests only.  The actual code runs in production without a hitch</p>