Add WebFlux redirect integration test case

Issue: SPR-15291

spring-webflux/src/test/java/org/springframework/web/reactive/result/method/annotation/RequestMappingViewResolutionIntegrationTests.java

@@ -16,10 +16,15 @@
 
 package org.springframework.web.reactive.result.method.annotation;
 
+import java.io.IOException;
+import java.net.HttpURLConnection;
+import java.net.Proxy;
 import java.net.URI;
+import java.net.URL;
 import java.util.Optional;
 
 import org.junit.Test;
+import reactor.core.publisher.Mono;
 
 import org.springframework.context.ApplicationContext;
 import org.springframework.context.annotation.AnnotationConfigApplicationContext;
@@ -30,16 +35,19 @@ import org.springframework.http.HttpStatus;
 import org.springframework.http.MediaType;
 import org.springframework.http.RequestEntity;
 import org.springframework.http.ResponseEntity;
+import org.springframework.http.client.SimpleClientHttpRequestFactory;
 import org.springframework.stereotype.Controller;
 import org.springframework.ui.Model;
 import org.springframework.web.bind.annotation.GetMapping;
 import org.springframework.web.bind.annotation.RequestParam;
+import org.springframework.web.client.RestTemplate;
 import org.springframework.web.reactive.config.ViewResolverRegistry;
 import org.springframework.web.reactive.config.WebFluxConfigurationSupport;
 import org.springframework.web.reactive.result.view.freemarker.FreeMarkerConfigurer;
 import org.springframework.web.server.ServerWebExchange;
 
-import static org.junit.Assert.*;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNull;
 
 /**
  * {@code @RequestMapping} integration tests with view resolution scenarios.
@@ -73,6 +81,25 @@ public class RequestMappingViewResolutionIntegrationTests extends AbstractReques
 		assertNull(response.getBody());
 	}
 
+	@Test // SPR-15291
+	public void redirect() throws Exception {
+		SimpleClientHttpRequestFactory factory = new SimpleClientHttpRequestFactory() {
+
+			@Override
+			protected void prepareConnection(HttpURLConnection conn, String method) throws IOException {
+				super.prepareConnection(conn, method);
+				conn.setInstanceFollowRedirects(false);
+			}
+		};
+
+		URI uri = new URI("http://localhost:" + this.port + "/redirect");
+		RequestEntity<Void> request = RequestEntity.get(uri).accept(MediaType.ALL).build();
+		ResponseEntity<Void> response = new RestTemplate(factory).exchange(request, Void.class);
+
+		assertEquals(HttpStatus.SEE_OTHER, response.getStatusCode());
+		assertEquals("/", response.getHeaders().getLocation().toString());
+	}
+
 
 	@Configuration
 	@ComponentScan(resourcePattern = "**/RequestMappingViewResolutionIntegrationTests$*.class")
@@ -108,6 +135,11 @@ public class RequestMappingViewResolutionIntegrationTests extends AbstractReques
 			model.addAttribute("hello", "Hello: " + name.orElse("<no name>") + "!");
 			return "test";
 		}
+
+		@GetMapping("/redirect")
+		public Mono<String> redirect() {
+			return Mono.just("redirect:/");
+		}
 	}
 
 }