Add mechanism to expose mock server results

WebTestClient is an actual client and generally it's only possible
to assert the client response (i.e. what goes over HTTP). However,
in a mock server scenario technically we have access to the server
request and response and can make those available for further
assertions.

This will be helpful for the WebTestClient integration with MockMvc
where many more assertions can be performed on the server request
and response when needed.

See gh-19647

spring-test/src/main/java/org/springframework/test/web/reactive/server/ExchangeResult.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -72,6 +72,9 @@ public class ExchangeResult {
 	@Nullable
 	private final String uriTemplate;
 
+	@Nullable
+	final Object mockServerResult;
+
 
 	/**
 	 * Create an instance with an HTTP request and response along with promises
@@ -83,9 +86,11 @@ public class ExchangeResult {
 	 * @param responseBody capture of serialized response body content
 	 * @param timeout how long to wait for content to materialize
 	 * @param uriTemplate the URI template used to set up the request, if any
+	 * @param serverResult the result of a mock server exchange if applicable.
 	 */
 	ExchangeResult(ClientHttpRequest request, ClientHttpResponse response,
-			Mono<byte[]> requestBody, Mono<byte[]> responseBody, Duration timeout, @Nullable String uriTemplate) {
+			Mono<byte[]> requestBody, Mono<byte[]> responseBody, Duration timeout, @Nullable String uriTemplate,
+			@Nullable Object serverResult) {
 
 		Assert.notNull(request, "ClientHttpRequest is required");
 		Assert.notNull(response, "ClientHttpResponse is required");
@@ -98,6 +103,7 @@ public class ExchangeResult {
 		this.responseBody = responseBody;
 		this.timeout = timeout;
 		this.uriTemplate = uriTemplate;
+		this.mockServerResult = serverResult;
 	}
 
 	/**
@@ -110,6 +116,7 @@ public class ExchangeResult {
 		this.responseBody = other.responseBody;
 		this.timeout = other.timeout;
 		this.uriTemplate = other.uriTemplate;
+		this.mockServerResult = other.mockServerResult;
 	}
 
 
@@ -195,6 +202,16 @@ public class ExchangeResult {
 		return this.responseBody.block(this.timeout);
 	}
 
+	/**
+	 * Return the result from the mock server exchange, if applicable, for
+	 * further assertions on the state of the server response.
+	 * @since 5.3
+	 * @see org.springframework.test.web.servlet.client.MockMvcTestClient#resultActionsFor(ExchangeResult)
+	 */
+	@Nullable
+	public Object getMockServerResult() {
+		return this.mockServerResult;
+	}
 
 	/**
 	 * Execute the given Runnable, catch any {@link AssertionError}, decorate
@@ -222,7 +239,8 @@ public class ExchangeResult {
 				"< " + getStatus() + " " + getStatus().getReasonPhrase() + "\n" +
 				"< " + formatHeaders(getResponseHeaders(), "\n< ") + "\n" +
 				"\n" +
-				formatBody(getResponseHeaders().getContentType(), this.responseBody) +"\n";
+				formatBody(getResponseHeaders().getContentType(), this.responseBody) +"\n" +
+				formatMockServerResult();
 	}
 
 	private String formatHeaders(HttpHeaders headers, String delimiter) {
@@ -252,4 +270,10 @@ public class ExchangeResult {
 				.block(this.timeout);
 	}
 
+	private String formatMockServerResult() {
+		return (this.mockServerResult != null ?
+				"\n======================  MockMvc (Server) ===============================\n" +
+						this.mockServerResult + "\n" : "");
+	}
+
 }

spring-test/src/main/java/org/springframework/test/web/reactive/server/MockServerClientHttpResponse.java

@@ -0,0 +1,35 @@
+/*
+ * Copyright 2002-2020 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
+ *
+ *      https://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.reactive.server;
+
+import org.springframework.http.client.reactive.ClientHttpResponse;
+
+/**
+ * Simple {@link ClientHttpResponse} extension that also exposes a result object
+ * from the underlying mock server exchange for further assertions on the state
+ * of the server response after the request is performed.
+ *
+ * @author Rossen Stoyanchev
+ * @since 5.3
+ */
+public interface MockServerClientHttpResponse extends ClientHttpResponse {
+
+	/**
+	 * Return the result object with the server request and response.
+	 */
+	Object getServerResult();
+
+}

spring-test/src/main/java/org/springframework/test/web/reactive/server/WiretapConnector.java

@@ -88,15 +88,16 @@ class WiretapConnector implements ClientHttpConnector {
 	 * Create the {@link ExchangeResult} for the given "request-id" header value.
 	 */
 	ExchangeResult getExchangeResult(String requestId, @Nullable String uriTemplate, Duration timeout) {
-		ClientExchangeInfo info = this.exchanges.remove(requestId);
-		Assert.state(info != null, () -> {
+		ClientExchangeInfo clientInfo = this.exchanges.remove(requestId);
+		Assert.state(clientInfo != null, () -> {
 			String header = WebTestClient.WEBTESTCLIENT_REQUEST_ID;
 			return "No match for " + header + "=" + requestId;
 		});
-		return new ExchangeResult(info.getRequest(), info.getResponse(),
-				info.getRequest().getRecorder().getContent(),
-				info.getResponse().getRecorder().getContent(),
-				timeout, uriTemplate);
+		return new ExchangeResult(clientInfo.getRequest(), clientInfo.getResponse(),
+				clientInfo.getRequest().getRecorder().getContent(),
+				clientInfo.getResponse().getRecorder().getContent(),
+				timeout, uriTemplate,
+				clientInfo.getResponse().getMockServerResult());
 	}
 
 
@@ -279,6 +280,12 @@ class WiretapConnector implements ClientHttpConnector {
 		public Flux<DataBuffer> getBody() {
 			return Flux.from(this.recorder.getPublisherToUse());
 		}
+
+		@Nullable
+		public Object getMockServerResult() {
+			return (getDelegate() instanceof MockServerClientHttpResponse ?
+					((MockServerClientHttpResponse) getDelegate()).getServerResult() : null);
+		}
 	}
 
 }