Add testing support for WebMvc.fn

This commit introduces testing support for WebMvc.fn in the form of a
RouterFunctionMockMvcBuilder and RouterFunctionMockMvcSpec.

Closes gh-30477

spring-test/src/main/java/org/springframework/test/web/servlet/client/MockMvcWebTestClient.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2022 the original author or authors.
+ * Copyright 2002-2024 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.
@@ -35,6 +35,7 @@
 import org.springframework.test.web.servlet.ResultMatcher;
 import org.springframework.test.web.servlet.setup.ConfigurableMockMvcBuilder;
 import org.springframework.test.web.servlet.setup.MockMvcConfigurer;
+import org.springframework.test.web.servlet.setup.RouterFunctionMockMvcBuilder;
 import org.springframework.test.web.servlet.setup.StandaloneMockMvcBuilder;
 import org.springframework.validation.Validator;
 import org.springframework.web.accept.ContentNegotiationManager;
@@ -47,6 +48,7 @@
 import org.springframework.web.servlet.LocaleResolver;
 import org.springframework.web.servlet.View;
 import org.springframework.web.servlet.ViewResolver;
+import org.springframework.web.servlet.function.RouterFunction;
 import org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping;
 import org.springframework.web.util.pattern.PathPatternParser;
 
@@ -81,13 +83,25 @@ public interface MockMvcWebTestClient {
 	 * Begin creating a {@link WebTestClient} by providing the {@code @Controller}
 	 * instance(s) to handle requests with.
 	 * <p>Internally this is delegated to and equivalent to using
-	 * {@link org.springframework.test.web.servlet.setup.MockMvcBuilders#standaloneSetup(Object...)}.
+	 * {@link org.springframework.test.web.servlet.setup.MockMvcBuilders#standaloneSetup(Object...)}
 	 * to initialize {@link MockMvc}.
 	 */
 	static ControllerSpec bindToController(Object... controllers) {
 		return new StandaloneMockMvcSpec(controllers);
 	}
 
+	/**
+	 * Begin creating a {@link WebTestClient} by providing the {@link RouterFunction}
+	 * instance(s) to handle requests with.
+	 * <p>Internally this is delegated to and equivalent to using
+	 * {@link org.springframework.test.web.servlet.setup.MockMvcBuilders#routerFunctions(RouterFunction[])}
+	 * to initialize {@link MockMvc}.
+	 * @since 6.2
+	 */
+	static RouterFunctionSpec bindToRouterFunction(RouterFunction<?>... routerFunctions) {
+		return new RouterFunctionMockMvcSpec(routerFunctions);
+	}
+
 	/**
 	 * Begin creating a {@link WebTestClient} by providing a
 	 * {@link WebApplicationContext} with Spring MVC infrastructure and
@@ -381,4 +395,72 @@ ControllerSpec mappedInterceptors(
 		ControllerSpec customHandlerMapping(Supplier<RequestMappingHandlerMapping> factory);
 	}
 
+
+	/**
+	 * Specification for configuring {@link MockMvc} to test one or more
+	 * {@linkplain RouterFunction router functions}
+	 * directly, and a simple facade around {@link RouterFunctionMockMvcBuilder}.
+	 * @since 6.2
+	 */
+	interface RouterFunctionSpec extends MockMvcServerSpec<RouterFunctionSpec> {
+
+		/**
+		 * Set the message converters to use.
+		 * <p>This is delegated to
+		 * {@link RouterFunctionMockMvcBuilder#setMessageConverters(HttpMessageConverter[])}.
+		 */
+		RouterFunctionSpec messageConverters(HttpMessageConverter<?>... messageConverters);
+
+		/**
+		 * Add global interceptors.
+		 * <p>This is delegated to
+		 * {@link RouterFunctionMockMvcBuilder#addInterceptors(HandlerInterceptor...)}.
+		 */
+		RouterFunctionSpec interceptors(HandlerInterceptor... interceptors);
+
+		/**
+		 * Add interceptors for specific patterns.
+		 * <p>This is delegated to
+		 * {@link RouterFunctionMockMvcBuilder#addMappedInterceptors(String[], HandlerInterceptor...)}.
+		 */
+		RouterFunctionSpec mappedInterceptors(
+				@Nullable String[] pathPatterns, HandlerInterceptor... interceptors);
+
+		/**
+		 * Specify the timeout value for async execution.
+		 * <p>This is delegated to
+		 * {@link RouterFunctionMockMvcBuilder#setAsyncRequestTimeout(long)}.
+		 */
+		RouterFunctionSpec asyncRequestTimeout(long timeout);
+
+		/**
+		 * Set the HandlerExceptionResolver types to use.
+		 * <p>This is delegated to
+		 * {@link RouterFunctionMockMvcBuilder#setHandlerExceptionResolvers(HandlerExceptionResolver...)}.
+		 */
+		RouterFunctionSpec handlerExceptionResolvers(HandlerExceptionResolver... exceptionResolvers);
+
+		/**
+		 * Set up view resolution.
+		 * <p>This is delegated to
+		 * {@link RouterFunctionMockMvcBuilder#setViewResolvers(ViewResolver...)}.
+		 */
+		RouterFunctionSpec viewResolvers(ViewResolver... resolvers);
+
+		/**
+		 * Set up a single {@link ViewResolver} with a fixed view.
+		 * <p>This is delegated to
+		 * {@link RouterFunctionMockMvcBuilder#setSingleView(View)}.
+		 */
+		RouterFunctionSpec singleView(View view);
+
+		/**
+		 * Enable URL path matching with parsed
+		 * {@link org.springframework.web.util.pattern.PathPattern PathPatterns}.
+		 * <p>This is delegated to
+		 * {@link RouterFunctionMockMvcBuilder#setPatternParser(PathPatternParser)}.
+		 */
+		RouterFunctionSpec patternParser(PathPatternParser parser);
+	}
+
 }

spring-test/src/main/java/org/springframework/test/web/servlet/client/RouterFunctionMockMvcSpec.java

@@ -0,0 +1,100 @@
+/*
+ * Copyright 2002-2024 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.servlet.client;
+
+import org.springframework.http.converter.HttpMessageConverter;
+import org.springframework.lang.Nullable;
+import org.springframework.test.web.servlet.setup.ConfigurableMockMvcBuilder;
+import org.springframework.test.web.servlet.setup.MockMvcBuilders;
+import org.springframework.test.web.servlet.setup.RouterFunctionMockMvcBuilder;
+import org.springframework.web.servlet.HandlerExceptionResolver;
+import org.springframework.web.servlet.HandlerInterceptor;
+import org.springframework.web.servlet.View;
+import org.springframework.web.servlet.ViewResolver;
+import org.springframework.web.servlet.function.RouterFunction;
+import org.springframework.web.util.pattern.PathPatternParser;
+
+/**
+ * Simple wrapper around a {@link RouterFunctionMockMvcBuilder} that implements
+ * {@link MockMvcWebTestClient.RouterFunctionSpec}.
+ *
+ * @author Arjen Poutsma
+ * @since 6.2
+ */
+class RouterFunctionMockMvcSpec extends AbstractMockMvcServerSpec<MockMvcWebTestClient.RouterFunctionSpec>
+		implements MockMvcWebTestClient.RouterFunctionSpec {
+
+	private final RouterFunctionMockMvcBuilder mockMvcBuilder;
+
+
+	RouterFunctionMockMvcSpec(RouterFunction<?>... routerFunctions) {
+		this.mockMvcBuilder = MockMvcBuilders.routerFunctions(routerFunctions);
+	}
+
+	@Override
+	public MockMvcWebTestClient.RouterFunctionSpec messageConverters(HttpMessageConverter<?>... messageConverters) {
+		this.mockMvcBuilder.setMessageConverters(messageConverters);
+		return this;
+	}
+
+	@Override
+	public MockMvcWebTestClient.RouterFunctionSpec interceptors(HandlerInterceptor... interceptors) {
+		mappedInterceptors(null, interceptors);
+		return this;
+	}
+
+	@Override
+	public MockMvcWebTestClient.RouterFunctionSpec mappedInterceptors(@Nullable String[] pathPatterns, HandlerInterceptor... interceptors) {
+		this.mockMvcBuilder.addMappedInterceptors(pathPatterns, interceptors);
+		return this;
+	}
+
+	@Override
+	public MockMvcWebTestClient.RouterFunctionSpec asyncRequestTimeout(long timeout) {
+		this.mockMvcBuilder.setAsyncRequestTimeout(timeout);
+		return this;
+	}
+
+	@Override
+	public MockMvcWebTestClient.RouterFunctionSpec handlerExceptionResolvers(HandlerExceptionResolver... exceptionResolvers) {
+		this.mockMvcBuilder.setHandlerExceptionResolvers(exceptionResolvers);
+		return this;
+	}
+
+	@Override
+	public MockMvcWebTestClient.RouterFunctionSpec viewResolvers(ViewResolver... resolvers) {
+		this.mockMvcBuilder.setViewResolvers(resolvers);
+		return this;
+	}
+
+	@Override
+	public MockMvcWebTestClient.RouterFunctionSpec singleView(View view) {
+		this.mockMvcBuilder.setSingleView(view);
+		return this;
+	}
+
+	@Override
+	public MockMvcWebTestClient.RouterFunctionSpec patternParser(PathPatternParser parser) {
+		this.mockMvcBuilder.setPatternParser(parser);
+		return this;
+	}
+
+	@Override
+	protected ConfigurableMockMvcBuilder<?> getMockMvcBuilder() {
+		return this.mockMvcBuilder;
+	}
+}

spring-test/src/main/java/org/springframework/test/web/servlet/setup/MockMvcBuilders.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2024 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.
@@ -19,6 +19,7 @@
 import org.springframework.test.web.servlet.MockMvc;
 import org.springframework.test.web.servlet.MockMvcBuilder;
 import org.springframework.web.context.WebApplicationContext;
+import org.springframework.web.servlet.function.RouterFunction;
 
 /**
  * The main class to import in order to access all available {@link MockMvcBuilder MockMvcBuilders}.
@@ -76,4 +77,23 @@ public static StandaloneMockMvcBuilder standaloneSetup(Object... controllers) {
 		return new StandaloneMockMvcBuilder(controllers);
 	}
 
+	/**
+	 * Build a {@link MockMvc} instance by registering one or more
+	 * {@link RouterFunction RouterFunction} instances and configuring Spring
+	 * MVC infrastructure programmatically.
+	 * <p>This allows full control over the instantiation and initialization of
+	 * router functions and their dependencies, similar to plain unit tests while
+	 * also making it possible to test one router function at a time.
+	 * <p>When this builder is used, the minimum infrastructure required by the
+	 * {@link org.springframework.web.servlet.DispatcherServlet DispatcherServlet}
+	 * to serve requests with router functions is created automatically
+	 * and can be customized, resulting in configuration that is equivalent to
+	 * what MVC Java configuration provides except using builder-style methods.
+	 * @param routerFunctions one or more {@code RouterFunction} instances to test
+	 * @since 6.2
+	 */
+	public static RouterFunctionMockMvcBuilder routerFunctions(RouterFunction<?>... routerFunctions) {
+		return new RouterFunctionMockMvcBuilder(routerFunctions);
+	}
+
 }