MockMvc - IllegalStateException: Async result for handler was not set during specified timeToWait=-1 [SPR-16869]

Adrian S opened SPR-16869 and commented

When trying to test Server-Sent Events endpoint created using rxjava2 and spring’s ReactiveTypeHandler you encounter:

java.lang.IllegalStateException: Async result for handler [io.reactivex.Flowable<java.lang.String> com.example.asyncssebug.MockMvcAsyncBugTest$TestApp.sse()] was not set during the specified timeToWait=-1java.lang.IllegalStateException: Async result for handler [io.reactivex.Flowable<java.lang.String> com.example.asyncssebug.MockMvcAsyncBugTest$TestApp.sse()] was not set during the specified timeToWait=-1
 at org.springframework.test.web.servlet.DefaultMvcResult.getAsyncResult(DefaultMvcResult.java:145) at org.springframework.test.web.servlet.DefaultMvcResult.getAsyncResult(DefaultMvcResult.java:136) at org.springframework.test.web.servlet.request.MockMvcRequestBuilders.asyncDispatch(MockMvcRequestBuilders.java:269)

Example test code to reproduce bug along with walkaround:

package com.example.asyncssebug;

import io.reactivex.Flowable;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.test.autoconfigure.web.servlet.AutoConfigureMockMvc;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.http.MediaType;
import org.springframework.test.context.junit4.SpringRunner;
import org.springframework.test.web.servlet.MockMvc;
import org.springframework.test.web.servlet.MvcResult;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import java.awt.*;
import java.util.concurrent.TimeUnit;

import static org.hamcrest.Matchers.nullValue;
import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.asyncDispatch;
import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.get;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.content;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.request;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;

@RunWith(SpringRunner.class)
@SpringBootTest(classes = MockMvcAsyncBugTest.TestApp.class)
@AutoConfigureMockMvc
public class MockMvcAsyncBugTest {

    @RestController
    @RequestMapping("/events")
    @SpringBootApplication
    public static class TestApp {

        @GetMapping(produces = MediaType.TEXT_EVENT_STREAM_VALUE)
        Flowable<String> sse() {
            return Flowable.intervalRange(0, 3, 0, 1, TimeUnit.SECONDS)
                    .map(aLong -> String.format("event%d", aLong));
        }
    }

    @Autowired
    MockMvc mockMvc;

    @Test
    public void failsWithIllegalStateExceptionAsyncResultForHandlerWasNotSetDuringSpecifiedTimeToWait() throws Exception {
        MvcResult mvcResult = mockMvc.perform(get("/events"))
                .andExpect(request().asyncStarted())
                .andExpect(status().isOk())
                .andReturn();

        mockMvc.perform(asyncDispatch(mvcResult))
                .andExpect(content().string("data:event0\n\ndata:event1\n\ndata:event2\n\n"));
    }

    @Test
    public void alsoFailsWithIllegalStateExceptionAsyncResultForHandlerWasNotSetDuringSpecifiedTimeToWait() throws Exception {
        mockMvc.perform(get("/events"))
                .andExpect(request().asyncStarted())
                .andExpect(request().asyncResult(nullValue()))
                .andExpect(status().isOk())
                .andExpect(content().string("data:event0\n\ndata:event1\n\ndata:event2\n\n"))
                .andReturn();
    }

    @Test
    public void walkaroundToMakeItWork() throws Exception {
        MvcResult mvcResult = mockMvc.perform(get("/events"))
                .andExpect(request().asyncStarted())
                .andExpect(status().isOk())
                .andReturn();
        mvcResult.getAsyncResult(5000L); // walkaround
        mockMvc.perform(asyncDispatch(mvcResult))
                .andExpect(content().string("data:event0\n\ndata:event1\n\ndata:event2\n\n"));
    }
}

Spring Boot version used is 2.0.2.RELEASE

Seems like default getAsyncResult(-1) instead of waiting forever doesn’t wait at all. As a walkaround you can add mvcResult.getAsyncResult(5000L) and then perform asyncDispatch on the mvcResult

Affects: 5.0.6

Referenced from: commits https://github.com/spring-projects/spring-framework/commit/2a993bf9ff7c9a4fbb1edef8ea1e7f96ac0a1afc, https://github.com/spring-projects/spring-framework/commit/9d36fd0b68883847260863cec7131d4e77720522