Only create a WebTestClient with WebFlux

This commit updates WebTestClientAutoConfiguration to only create a
WebTestClient when running a WebFlux-based application as mocking the
context only works with that mode at the moment.

Closes gh-12318

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

@@ -6520,6 +6520,9 @@ example shows a class that uses both `@WebFluxTest` and a `WebTestClient`:
 	}
 ----
 
+TIP: This setup is only supported by WebFlux applications as using `WebTestClient` in a
+mocked web application only works with WebFlux at the moment.
+
 A list of the auto-configuration that is enabled by `@WebFluxTest` can be
 <<appendix-test-auto-configuration#test-auto-configuration,found in the appendix>>.
 

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

@@ -29,7 +29,8 @@ import org.springframework.boot.test.autoconfigure.properties.PropertyMapping;
 import org.springframework.test.web.reactive.server.WebTestClient;
 
 /**
- * Annotation that can be applied to a test class to enable a {@link WebTestClient}.
+ * Annotation that can be applied to a test class to enable a {@link WebTestClient}. At
+ * the moment, only WebFlux applications are supported.
  *
  * @author Stephane Nicoll
  * @since 2.0.0

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

@@ -22,9 +22,11 @@ import java.util.List;
 
 import org.springframework.beans.factory.ObjectProvider;
 import org.springframework.boot.autoconfigure.AutoConfigureAfter;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnBean;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
 import org.springframework.boot.autoconfigure.http.codec.CodecsAutoConfiguration;
+import org.springframework.boot.autoconfigure.web.reactive.WebFluxAutoConfiguration;
 import org.springframework.boot.context.properties.ConfigurationProperties;
 import org.springframework.boot.context.properties.EnableConfigurationProperties;
 import org.springframework.boot.web.codec.CodecCustomizer;
@@ -33,6 +35,7 @@ import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.test.web.reactive.server.WebTestClient;
 import org.springframework.web.reactive.function.client.WebClient;
+import org.springframework.web.server.WebHandler;
 
 /**
  * Auto-configuration for {@link WebTestClient}.
@@ -43,12 +46,13 @@ import org.springframework.web.reactive.function.client.WebClient;
  */
 @Configuration
 @ConditionalOnClass({ WebClient.class, WebTestClient.class })
-@AutoConfigureAfter(CodecsAutoConfiguration.class)
+@AutoConfigureAfter({ CodecsAutoConfiguration.class, WebFluxAutoConfiguration.class })
 @EnableConfigurationProperties
 public class WebTestClientAutoConfiguration {
 
 	@Bean
 	@ConditionalOnMissingBean
+	@ConditionalOnBean(WebHandler.class)
 	public WebTestClient webTestClient(ApplicationContext applicationContext,
 			List<WebTestClientBuilderCustomizer> customizers) {
 		WebTestClient.Builder builder = WebTestClient

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

@@ -18,18 +18,15 @@ package org.springframework.boot.test.autoconfigure.web.reactive;
 
 import java.time.Duration;
 import java.time.temporal.ChronoUnit;
-import java.util.Collections;
 
-import org.junit.After;
 import org.junit.Test;
 
+import org.springframework.boot.autoconfigure.AutoConfigurations;
+import org.springframework.boot.test.context.runner.ApplicationContextRunner;
 import org.springframework.boot.web.codec.CodecCustomizer;
-import org.springframework.context.annotation.AnnotationConfigApplicationContext;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.context.annotation.Import;
-import org.springframework.core.env.MapPropertySource;
-import org.springframework.core.env.PropertySource;
 import org.springframework.http.codec.CodecConfigurer;
 import org.springframework.test.util.ReflectionTestUtils;
 import org.springframework.test.web.reactive.server.WebTestClient;
@@ -44,50 +41,43 @@ import static org.mockito.Mockito.verify;
  * Tests for {@link WebTestClientAutoConfiguration}
  *
  * @author Brian Clozel
+ * @author Stephane Nicoll
  */
 public class WebTestClientAutoConfigurationTests {
 
-	private AnnotationConfigApplicationContext context;
+	private ApplicationContextRunner contextRunner = new ApplicationContextRunner()
+			.withConfiguration(AutoConfigurations.of(
+					WebTestClientAutoConfiguration.class));
 
-	@After
-	public void close() {
-		if (this.context != null) {
-			this.context.close();
-		}
+	@Test
+	public void shouldNotBeConfiguredWithoutWebHandler() {
+		this.contextRunner.run((context) -> {
+			assertThat(context).hasNotFailed();
+			assertThat(context).doesNotHaveBean(WebTestClient.class);
+		});
 	}
 
 	@Test
 	public void shouldCustomizeClientCodecs() {
-		load(CodecConfiguration.class);
-		WebTestClient webTestClient = this.context.getBean(WebTestClient.class);
-		CodecCustomizer codecCustomizer = this.context.getBean(CodecCustomizer.class);
-		assertThat(webTestClient).isNotNull();
-		verify(codecCustomizer).customize(any(CodecConfigurer.class));
+		this.contextRunner.withUserConfiguration(CodecConfiguration.class)
+				.run((context) -> {
+					assertThat(context).hasSingleBean(WebTestClient.class);
+					assertThat(context).hasSingleBean(CodecCustomizer.class);
+					verify(context.getBean(CodecCustomizer.class)).customize(
+							any(CodecConfigurer.class));
+				});
 	}
 
 	@Test
 	public void shouldCustomizeTimeout() {
-		PropertySource<?> propertySource = new MapPropertySource("test", Collections
-				.singletonMap("spring.test.webtestclient.timeout", (Object) "PT15M"));
-		load(propertySource, BaseConfiguration.class);
-		WebTestClient webTestClient = this.context.getBean(WebTestClient.class);
-		Object duration = ReflectionTestUtils.getField(webTestClient, "timeout");
+		this.contextRunner.withUserConfiguration(BaseConfiguration.class)
+				.withPropertyValues("spring.test.webtestclient.timeout=15m")
+				.run((context) -> {
+					WebTestClient webTestClient = context.getBean(WebTestClient.class);
+					Object duration = ReflectionTestUtils.getField(webTestClient,
+							"timeout");
 					assertThat(duration).isEqualTo(Duration.of(15, ChronoUnit.MINUTES));
-	}
-
-	private void load(Class<?>... config) {
-		load(null, config);
-	}
-
-	private void load(PropertySource<?> propertySource, Class<?>... config) {
-		AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext();
-		if (propertySource != null) {
-			context.getEnvironment().getPropertySources().addFirst(propertySource);
-		}
-		context.register(config);
-		context.register(WebTestClientAutoConfiguration.class);
-		context.refresh();
-		this.context = context;
+				});
 	}
 
 	@Configuration