String body = mockMvc.perform(bla... bla).andReturn().getResolvedException().getMessage()

这将为您提供响应的主体。“用户名已被占用”在你的情况下。

Spring MockMvc现在直接支持JSON。所以你只需说:

.andExpect(content().json("{'message':'ok'}"));

与字符串比较不同，它会说“缺少字段xyz”或“消息预期'ok'得到'nok'”之类的东西。

该方法是在Spring 4.1中引入的。

这里有一种更优雅的方式

mockMvc.perform(post("/retrieve?page=1&countReg=999999")
            .header("Authorization", "Bearer " + validToken))
            .andExpect(status().isOk())
            .andExpect(content().string(containsString("regCount")));

下面是一个例子，如何解析JSON响应，甚至如何以JSON形式发送一个bean请求:

  @Autowired
  protected MockMvc mvc;

  private static final ObjectMapper MAPPER = new ObjectMapper()
    .configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, false)
    .configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false)
    .registerModule(new JavaTimeModule());

  public static String requestBody(Object request) {
    try {
      return MAPPER.writeValueAsString(request);
    } catch (JsonProcessingException e) {
      throw new RuntimeException(e);
    }
  }

  public static <T> T parseResponse(MvcResult result, Class<T> responseClass) {
    try {
      String contentAsString = result.getResponse().getContentAsString();
      return MAPPER.readValue(contentAsString, responseClass);
    } catch (IOException e) {
      throw new RuntimeException(e);
    }
  }

  @Test
  public void testUpdate() {
    Book book = new Book();
    book.setTitle("1984");
    book.setAuthor("Orwell");
    MvcResult requestResult = mvc.perform(post("http://example.com/book/")
      .contentType(MediaType.APPLICATION_JSON)
      .content(requestBody(book)))
      .andExpect(status().isOk())
      .andReturn();
    UpdateBookResponse updateBookResponse = parseResponse(requestResult, UpdateBookResponse.class);
    assertEquals("1984", updateBookResponse.getTitle());
    assertEquals("Orwell", updateBookResponse.getAuthor());
  }

正如您在这里看到的，Book是一个请求DTO, UpdateBookResponse是一个从JSON解析的响应对象。您可能想要更改Jackson的ObjectMapper配置。

摘自spring教程

mockMvc.perform(get("/" + userName + "/bookmarks/" 
    + this.bookmarkList.get(0).getId()))
    .andExpect(status().isOk())
    .andExpect(content().contentType(contentType))
    .andExpect(jsonPath("$.id", is(this.bookmarkList.get(0).getId().intValue())))
    .andExpect(jsonPath("$.uri", is("http://bookmark.com/1/" + userName)))
    .andExpect(jsonPath("$.description", is("A description")));

是可以从import static org.hamcrest.Matchers.*;

jsonPath可从导入静态org.springframework.test.web.servlet.result.MockMvcResultMatchers.jsonPath;

和jsonPath引用可以在这里找到

Spring security的@WithMockUser和hamcrest的containsString匹配器提供了一个简单而优雅的解决方案:

@Test
@WithMockUser(roles = "USER")
public void loginWithRoleUserThenExpectUserSpecificContent() throws Exception {
    mockMvc.perform(get("/index"))
            .andExpect(status().isOk())
            .andExpect(content().string(containsString("This content is only shown to users.")));
}

更多的例子在github上