Bind WebTestClient to the default WebHandler

Previously, if multiple WebHandler beans were present, the auto-config
for WebTestClient fail to identify a suitable candidate as it expects
to only have such a bean.

This commit updates the logic to look for a well-known bean name that
WebFlux uses, and clarify the exception message to state that a bean
with a given name is expected to be found.

The exception message has been further refined to mention that, if
such a bean is not present, then a MockMVc-compatible ApplicationContext
should be available (i.e. WebApplicationContext).

Closes gh-47617

module/spring-boot-webtestclient/src/main/java/org/springframework/boot/webtestclient/WebTestClientAutoConfiguration.java

@@ -18,7 +18,6 @@ package org.springframework.boot.webtestclient;
 
 import java.util.List;
 
-import org.springframework.beans.factory.NoSuchBeanDefinitionException;
 import org.springframework.beans.factory.ObjectProvider;
 import org.springframework.boot.autoconfigure.AutoConfiguration;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
@@ -40,7 +39,7 @@ import org.springframework.test.web.servlet.client.MockMvcWebTestClient;
 import org.springframework.util.ClassUtils;
 import org.springframework.web.context.WebApplicationContext;
 import org.springframework.web.reactive.function.client.WebClient;
-import org.springframework.web.server.WebHandler;
+import org.springframework.web.server.adapter.WebHttpHandlerBuilder;
 
 /**
  * Auto-configuration for {@link WebTestClient}.
@@ -79,31 +78,22 @@ public final class WebTestClientAutoConfiguration {
 		if (baseUrl != null) {
 			return WebTestClient.bindToServer().uriBuilderFactory(BaseUrlUriBuilderFactory.get(baseUrl));
 		}
-		if (hasBean(applicationContext, WebHandler.class)) {
+		if (applicationContext.containsBean(WebHttpHandlerBuilder.WEB_HANDLER_BEAN_NAME)) {
 			MockServerSpec<?> spec = WebTestClient.bindToApplicationContext(applicationContext);
 			configurers.forEach(spec::apply);
 			return spec.configureClient();
 		}
 		if (ClassUtils.isPresent(WEB_APPLICATION_CONTEXT_CLASS, applicationContext.getClassLoader())) {
-			if (hasBean(applicationContext, MockMvc.class)) {
-				return MockMvcWebTestClient.bindTo(applicationContext.getBean(MockMvc.class));
+			MockMvc mockMvc = applicationContext.getBeanProvider(MockMvc.class).getIfUnique();
+			if (mockMvc != null) {
+				return MockMvcWebTestClient.bindTo(mockMvc);
 			}
 			if (applicationContext instanceof WebApplicationContext webApplicationContext) {
 				return MockMvcWebTestClient.bindToApplicationContext(webApplicationContext).configureClient();
 			}
 		}
 		throw new IllegalStateException(
-				"Mock WebTestClient support requires a WebHandler or MockMvc bean and neither was present");
-	}
-
-	private boolean hasBean(ApplicationContext applicationContext, Class<?> type) {
-		try {
-			applicationContext.getBean(type);
-			return true;
-		}
-		catch (NoSuchBeanDefinitionException ex) {
-			return false;
-		}
+				"Mock WebTestClient support requires a WebHandler (named 'webHandler') bean or a WebApplicationContext and neither was present");
 	}
 
 }

module/spring-boot-webtestclient/src/test/java/org/springframework/boot/webflux/test/autoconfigure/WebTestClientAutoConfigurationTests.java

@@ -71,6 +71,31 @@ class WebTestClientAutoConfigurationTests {
 		});
 	}
 
+	@Test
+	void shouldFailWhenDefaultWebHandlerIsNotAvailable() {
+		this.contextRunner.withBean("myWebHandler", WebHandler.class, () -> mock(WebHandler.class)).run((context) -> {
+			assertThat(context).hasFailed();
+			assertThat(context).getFailure()
+				.rootCause()
+				.isInstanceOf(RuntimeException.class)
+				.hasMessageStartingWith("Mock WebTestClient support requires")
+				.hasMessageContaining("WebHandler");
+		});
+	}
+
+	@Test
+	void shouldFailWithNeitherDefaultWebHandlerNorWebApplicationContext() {
+		ClassLoader parentClassLoader = Thread.currentThread().getContextClassLoader();
+		this.contextRunner.withClassLoader(new FilteredClassLoader(parentClassLoader, WebApplicationContext.class))
+			.run((context) -> {
+				assertThat(context).getFailure()
+					.rootCause()
+					.isInstanceOf(RuntimeException.class)
+					.hasMessageStartingWith("Mock WebTestClient support requires")
+					.hasMessageContaining("WebApplicationContext");
+			});
+	}
+
 	@Test
 	@WithResource(name = "META-INF/spring.factories", content = """
 			org.springframework.boot.test.http.server.BaseUrlProvider=\

smoke-test/spring-boot-smoke-test-webflux/src/test/java/smoketest/webflux/SampleWebFluxApplicationIntegrationTests.java

@@ -0,0 +1,114 @@
+/*
+ * Copyright 2012-present 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 smoketest.webflux;
+
+import org.junit.jupiter.api.Test;
+import reactor.core.publisher.Mono;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.boot.test.context.SpringBootTest.WebEnvironment;
+import org.springframework.boot.webtestclient.AutoConfigureWebTestClient;
+import org.springframework.http.HttpStatus;
+import org.springframework.http.MediaType;
+import org.springframework.test.web.reactive.server.WebTestClient;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Basic integration tests for WebFlux application.
+ *
+ * @author Brian Clozel
+ */
+@SpringBootTest(webEnvironment = WebEnvironment.RANDOM_PORT, properties = "server.error.include-message=always")
+@AutoConfigureWebTestClient
+class SampleWebFluxApplicationIntegrationTests {
+
+	@Autowired
+	private WebTestClient webClient;
+
+	@Test
+	void testWelcome() {
+		this.webClient.get()
+			.uri("/")
+			.accept(MediaType.TEXT_PLAIN)
+			.exchange()
+			.expectBody(String.class)
+			.isEqualTo("Hello World");
+	}
+
+	@Test
+	void testEcho() {
+		this.webClient.post()
+			.uri("/echo")
+			.contentType(MediaType.TEXT_PLAIN)
+			.accept(MediaType.TEXT_PLAIN)
+			.body(Mono.just("Hello WebFlux!"), String.class)
+			.exchange()
+			.expectBody(String.class)
+			.isEqualTo("Hello WebFlux!");
+	}
+
+	@Test
+	void testActuatorStatus() {
+		this.webClient.get()
+			.uri("/actuator/health")
+			.accept(MediaType.APPLICATION_JSON)
+			.exchange()
+			.expectStatus()
+			.isOk()
+			.expectBody()
+			.json("{\"status\":\"UP\"}");
+	}
+
+	@Test
+	void templated404ErrorPage() {
+		this.webClient.get()
+			.uri("/404")
+			.accept(MediaType.TEXT_HTML)
+			.exchange()
+			.expectStatus()
+			.isNotFound()
+			.expectBody(String.class)
+			.value((body) -> assertThat(body).isEqualToNormalizingNewlines("404 page\n"));
+	}
+
+	@Test
+	void templated4xxErrorPage() {
+		this.webClient.get()
+			.uri("/bad-request")
+			.accept(MediaType.TEXT_HTML)
+			.exchange()
+			.expectStatus()
+			.isBadRequest()
+			.expectBody(String.class)
+			.value((body) -> assertThat(body).isEqualToNormalizingNewlines("4xx page\n"));
+	}
+
+	@Test
+	void htmlErrorPage() {
+		this.webClient.get()
+			.uri("/five-hundred")
+			.accept(MediaType.TEXT_HTML)
+			.exchange()
+			.expectStatus()
+			.isEqualTo(HttpStatus.INTERNAL_SERVER_ERROR)
+			.expectBody(String.class)
+			.value((body) -> assertThat(body).contains("status: 500").contains("message: Expected!"));
+	}
+
+}

smoke-test/spring-boot-smoke-test-webflux/src/test/java/smoketest/webflux/SampleWebFluxApplicationTests.java

@@ -16,13 +16,15 @@
 
 package smoketest.webflux;
 
+import java.util.Map;
+
 import org.junit.jupiter.api.Test;
 import reactor.core.publisher.Mono;
 
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.boot.test.context.SpringBootTest;
-import org.springframework.boot.test.context.SpringBootTest.WebEnvironment;
 import org.springframework.boot.webtestclient.AutoConfigureWebTestClient;
+import org.springframework.core.ParameterizedTypeReference;
 import org.springframework.http.HttpStatus;
 import org.springframework.http.MediaType;
 import org.springframework.test.web.reactive.server.WebTestClient;
@@ -30,27 +32,21 @@ import org.springframework.test.web.reactive.server.WebTestClient;
 import static org.assertj.core.api.Assertions.assertThat;
 
 /**
- * Basic integration tests for WebFlux application.
+ * Basic tests for a WebFlux application, configuring the {@link WebTestClient} to test
+ * without a running server.
  *
- * @author Brian Clozel
+ * @author Stephane Nicoll
  */
-@SpringBootTest(webEnvironment = WebEnvironment.RANDOM_PORT, properties = "server.error.include-message=always")
+@SpringBootTest
 @AutoConfigureWebTestClient
 class SampleWebFluxApplicationTests {
 
+	private static final ParameterizedTypeReference<Map<String, Object>> MAP_TYPE = new ParameterizedTypeReference<Map<String, Object>>() {
+	};
+
 	@Autowired
 	private WebTestClient webClient;
 
-	@Test
-	void testWelcome() {
-		this.webClient.get()
-			.uri("/")
-			.accept(MediaType.TEXT_PLAIN)
-			.exchange()
-			.expectBody(String.class)
-			.isEqualTo("Hello World");
-	}
-
 	@Test
 	void testEcho() {
 		this.webClient.post()
@@ -64,51 +60,27 @@ class SampleWebFluxApplicationTests {
 	}
 
 	@Test
-	void testActuatorStatus() {
+	void testBadRequest() {
 		this.webClient.get()
-			.uri("/actuator/health")
+			.uri("/bad-request")
 			.accept(MediaType.APPLICATION_JSON)
 			.exchange()
 			.expectStatus()
-			.isOk()
-			.expectBody()
-			.json("{\"status\":\"UP\"}");
-	}
-
-	@Test
-	void templated404ErrorPage() {
-		this.webClient.get()
-			.uri("/404")
-			.accept(MediaType.TEXT_HTML)
-			.exchange()
-			.expectStatus()
-			.isNotFound()
-			.expectBody(String.class)
-			.value((body) -> assertThat(body).isEqualToNormalizingNewlines("404 page\n"));
-	}
-
-	@Test
-	void templated4xxErrorPage() {
-		this.webClient.get()
-			.uri("/bad-request")
-			.accept(MediaType.TEXT_HTML)
-			.exchange()
-			.expectStatus()
 			.isBadRequest()
-			.expectBody(String.class)
-			.value((body) -> assertThat(body).isEqualToNormalizingNewlines("4xx page\n"));
+			.expectBody(MAP_TYPE)
+			.value((content) -> assertThat(content).containsEntry("path", "/bad-request"));
 	}
 
 	@Test
-	void htmlErrorPage() {
+	void testServerError() {
 		this.webClient.get()
 			.uri("/five-hundred")
-			.accept(MediaType.TEXT_HTML)
+			.accept(MediaType.APPLICATION_JSON)
 			.exchange()
 			.expectStatus()
 			.isEqualTo(HttpStatus.INTERNAL_SERVER_ERROR)
-			.expectBody(String.class)
-			.value((body) -> assertThat(body).contains("status: 500").contains("message: Expected!"));
+			.expectBody(MAP_TYPE)
+			.value((content) -> assertThat(content).containsEntry("path", "/five-hundred"));
 	}
 
 }