Respect async request timeout of -1 in MockMvc

When falling back on the timeout associated with the async request,
a value of -1 must be treated as: never time out.

Issue: SPR-16869

spring-test/src/test/java/org/springframework/test/web/servlet/samples/standalone/ReactiveReturnTypeTests.java

@@ -0,0 +1,68 @@
+/*
+ * Copyright 2002-2018 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.test.web.servlet.samples.standalone;
+
+import java.time.Duration;
+
+import org.junit.Test;
+import reactor.core.publisher.Flux;
+
+import org.springframework.http.MediaType;
+import org.springframework.test.web.servlet.MockMvc;
+import org.springframework.test.web.servlet.MvcResult;
+import org.springframework.test.web.servlet.setup.MockMvcBuilders;
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.RestController;
+
+import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.*;
+import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.*;
+import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.request;
+
+/**
+ * Tests with reactive return value types.
+ *
+ * @author Rossen Stoyanchev
+ */
+public class ReactiveReturnTypeTests {
+
+
+	@Test // SPR-16869
+	public void sseWithFlux() throws Exception {
+
+		MockMvc mockMvc = MockMvcBuilders.standaloneSetup(ReactiveController.class).build();
+
+		MvcResult mvcResult = mockMvc.perform(get("/spr16869"))
+				.andExpect(request().asyncStarted())
+				.andExpect(status().isOk())
+				.andReturn();
+
+		mockMvc.perform(asyncDispatch(mvcResult))
+				.andExpect(content().string("data:event0\n\ndata:event1\n\ndata:event2\n\n"));
+	}
+
+
+
+	@RestController
+	static class ReactiveController {
+
+		@GetMapping(path = "/spr16869", produces = MediaType.TEXT_EVENT_STREAM_VALUE)
+		Flux<String> sseFlux() {
+			return Flux.interval(Duration.ofSeconds(1)).take(3)
+					.map(aLong -> String.format("event%d", aLong));
+		}
+	}
+
+}