Add an example showing how to use Spring REST Docs with WebTestClient

See gh-15978

Author: nosan

spring-boot-project/spring-boot-docs/src/main/asciidoc/spring-boot-features.adoc

@@ -7716,7 +7716,25 @@ bean can be used, as shown in the following example:
 include::{code-examples}/test/autoconfigure/restdocs/restassured/AdvancedConfigurationExample.java[tag=configuration]
 ----
 
+[[boot-features-testing-spring-boot-applications-testing-autoconfigured-rest-docs-web-test-client]]
+===== Auto-configured Spring REST Docs Tests with WebTestClient
+`@AutoConfigureRestDocs` could be used in conjunction with a `@WebFluxTest` to generate REST Docs.
+`@AutoConfigureRestDocs` customizes the `WebTestClient` bean to use Spring REST Docs. You can
+inject it by using `@Autowired` and use it in your tests. Here is a quick sample:
 
+[source,java,indent=0]
+----
+include::{code-examples}/test/autoconfigure/restdocs/webclient/UsersDocumentationTests.java[tag=source]
+----
+
+If you require more control over Spring REST Docs configuration than offered by the
+attributes of `@AutoConfigureRestDocs`, you can use a
+`RestDocsWebTestClientConfigurationCustomizer` bean, as shown in the following example:
+
+[source,java,indent=0]
+----
+include::{code-examples}/test/autoconfigure/restdocs/webclient/AdvancedRestDocsWebTestClientConfigurationExample.java[tag=configuration]
+----
 
 [[boot-features-testing-spring-boot-applications-testing-auto-configured-additional-auto-config]]
 ==== Additional Auto-configuration and Slicing

spring-boot-project/spring-boot-docs/src/main/java/org/springframework/boot/docs/test/autoconfigure/restdocs/webclient/AdvancedRestDocsWebTestClientConfigurationExample.java

@@ -0,0 +1,37 @@
+/*
+ * Copyright 2012-2019 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.boot.docs.test.autoconfigure.restdocs.webclient;
+
+import org.springframework.boot.test.autoconfigure.restdocs.RestDocsWebTestClientConfigurationCustomizer;
+import org.springframework.boot.test.context.TestConfiguration;
+import org.springframework.restdocs.webtestclient.WebTestClientRestDocumentationConfigurer;
+
+public class AdvancedRestDocsWebTestClientConfigurationExample {
+
+	// tag::configuration[]
+	@TestConfiguration
+	static class CustomizationConfiguration
+			implements RestDocsWebTestClientConfigurationCustomizer {
+
+		@Override
+		public void customize(WebTestClientRestDocumentationConfigurer configurer) {
+			configurer.snippets().withEncoding("UTF-8");
+		}
+
+	}
+	// end::configuration[]
+
+}

spring-boot-project/spring-boot-docs/src/main/java/org/springframework/boot/docs/test/autoconfigure/restdocs/webclient/UsersDocumentationTests.java

@@ -0,0 +1,47 @@
+/*
+ * Copyright 2012-2019 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.boot.docs.test.autoconfigure.restdocs.webclient;
+
+// tag::source[]
+
+import org.junit.jupiter.api.Test;
+import org.junit.runner.RunWith;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.autoconfigure.restdocs.AutoConfigureRestDocs;
+import org.springframework.boot.test.autoconfigure.web.reactive.WebFluxTest;
+import org.springframework.test.context.junit4.SpringRunner;
+import org.springframework.test.web.reactive.server.WebTestClient;
+
+import static org.springframework.restdocs.webtestclient.WebTestClientRestDocumentation.document;
+
+@RunWith(SpringRunner.class)
+@WebFluxTest
+@AutoConfigureRestDocs
+public class UsersDocumentationTests {
+
+	@Autowired
+	private WebTestClient webTestClient;
+
+	@Test
+	void listUsers() {
+		this.webTestClient.get().uri("/").exchange().expectStatus().isOk().expectBody()
+				.consumeWith(document("list-users"));
+
+	}
+
+}
+// end::source[]