Async Requests

This section shows how to use MockMvc on its own to test asynchronous request handling. If using MockMvc through the WebTestClient, there is nothing special to do to make asynchronous requests work as the WebTestClient automatically does what is described in this section.

Servlet asynchronous requests, supported in Web MVC, work by exiting the Servlet container thread and allowing the application to compute the response asynchronously, after which an async dispatch is made to complete processing on a Servlet container thread.

In Web MVC Test, async requests can be tested by asserting the produced async value first, then manually performing the async dispatch, and finally verifying the response. Below is an example test for controller methods that return DeferredResult, Callable, or reactive type such as Reactor Mono:

// static import of MockMvcRequestBuilders.* and MockMvcResultMatchers.*

@Test
void test() throws Exception {
    MvcResult mvcResult = this.mockMvc.perform(get("/path"))
          .andExpect(status().isOk()) (1)
          .andExpect(request().asyncStarted()) (2)
          .andExpect(request().asyncResult("body")) (3)
          .andReturn();

    this.mockMvc.perform(asyncDispatch(mvcResult)) (4)
          .andExpect(status().isOk()) (5)
          .andExpect(content().string("body"));
}

1	Check response status is still unchanged
2	Async processing must have started
3	Wait and assert the async result
4	Manually perform an ASYNC dispatch (as there is no running container)
5	Verify the final response