Add shortcut to mutate + apply to WebTestClient

Issue: SPR-15770

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

@@ -141,6 +141,11 @@ class DefaultWebTestClient implements WebTestClient {
 		return this.builder;
 	}
 
+	@Override
+	public WebTestClient mutateWith(WebTestClientConfigurer configurer) {
+		return mutate().apply(configurer).build();
+	}
+
 
 	private class DefaultRequestBodyUriSpec implements RequestBodyUriSpec {
 

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

@@ -135,12 +135,23 @@ public interface WebTestClient {
 	RequestBodyUriSpec method(HttpMethod method);
 
 
-
 	/**
 	 * Return a builder to mutate properties of this web test client.
 	 */
 	Builder mutate();
 
+	/**
+	 * Mutate the {@link WebTestClient}, apply the given configurer, and build
+	 * a new instance. Essentially a shortcut for:
+	 * <pre>
+	 * mutate().apply(configurer).build();
+	 * </pre>
+	 * @param configurer the configurer to apply
+	 * @return the mutated test client
+	 */
+	WebTestClient mutateWith(WebTestClientConfigurer configurer);
+
+
 	// Static, factory methods
 
 	/**