Clarify that @AutoConfigureWebTestClient uses mock infrastructure

Closes gh-29890

Author: wilkinsona

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

@@ -200,7 +200,7 @@ For convenience, tests that need to make REST calls to the started server can ad
 
 include::code:MyRandomPortWebTestClientTests[]
 
-TIP: `WebTestClient` can be used against both live servers and <<features#features.testing.spring-boot-applications.with-mock-environment, mock environments>>.
+TIP: `WebTestClient` can also used with a <<features#features.testing.spring-boot-applications.with-mock-environment, mock environment>>, removing the need for a running server, by annotating your test class with `@AutoConfigureWebTestClient`.
 
 This setup requires `spring-webflux` on the classpath.
 If you can not or will not add webflux, Spring Boot also provides a `TestRestTemplate` facility:

spring-boot-project/spring-boot-test-autoconfigure/src/main/java/org/springframework/boot/test/autoconfigure/web/reactive/AutoConfigureWebTestClient.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2019 the original author or authors.
+ * Copyright 2012-2032 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.
@@ -26,15 +26,18 @@
 
 import org.springframework.boot.autoconfigure.ImportAutoConfiguration;
 import org.springframework.boot.test.autoconfigure.properties.PropertyMapping;
+import org.springframework.context.ApplicationContext;
 import org.springframework.test.web.reactive.server.WebTestClient;
 
 /**
- * Annotation that can be applied to a test class to enable a {@link WebTestClient}. At
- * the moment, only WebFlux applications are supported.
+ * Annotation that can be applied to a test class to enable a {@link WebTestClient} that
+ * is bound directly to the application. Tests do not rely upon an HTTP server and use
+ * mock requests and responses. At the moment, only WebFlux applications are supported.
  *
  * @author Stephane Nicoll
  * @since 2.0.0
  * @see WebTestClientAutoConfiguration
+ * @see WebTestClient#bindToApplicationContext(ApplicationContext)
  */
 @Target({ ElementType.TYPE, ElementType.METHOD })
 @Retention(RetentionPolicy.RUNTIME)