Add error rendering support with @WebFluxTest

See gh-16266

spring-boot-project/spring-boot-test-autoconfigure/src/main/resources/META-INF/spring.factories

@@ -100,7 +100,8 @@ org.springframework.boot.autoconfigure.http.codec.CodecsAutoConfiguration,\
 org.springframework.boot.autoconfigure.mustache.MustacheAutoConfiguration,\
 org.springframework.boot.autoconfigure.thymeleaf.ThymeleafAutoConfiguration,\
 org.springframework.boot.autoconfigure.validation.ValidationAutoConfiguration,\
-org.springframework.boot.autoconfigure.web.reactive.WebFluxAutoConfiguration
+org.springframework.boot.autoconfigure.web.reactive.WebFluxAutoConfiguration,\
+org.springframework.boot.autoconfigure.web.reactive.error.ErrorWebFluxAutoConfiguration
 
 # AutoConfigureMockMvc auto-configuration imports
 org.springframework.boot.test.autoconfigure.web.servlet.AutoConfigureMockMvc=\

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

@@ -18,6 +18,8 @@ package org.springframework.boot.test.autoconfigure.web.reactive.webclient;
 import reactor.core.publisher.Mono;
 
 import org.springframework.boot.test.autoconfigure.web.reactive.WebFluxTest;
+import org.springframework.core.Ordered;
+import org.springframework.core.annotation.Order;
 import org.springframework.http.HttpStatus;
 import org.springframework.stereotype.Component;
 import org.springframework.web.server.ServerWebExchange;
@@ -27,8 +29,10 @@ import org.springframework.web.server.WebExceptionHandler;
  * Example {@link WebExceptionHandler} used with {@link WebFluxTest} tests.
  *
  * @author Madhura Bhave
+ * @author Ali Dehghani
  */
 @Component
+@Order(Ordered.HIGHEST_PRECEDENCE)
 public class ExampleWebExceptionHandler implements WebExceptionHandler {
 
 	@Override

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

@@ -25,6 +25,7 @@ import org.springframework.boot.autoconfigure.freemarker.FreeMarkerAutoConfigura
 import org.springframework.boot.autoconfigure.mustache.MustacheAutoConfiguration;
 import org.springframework.boot.autoconfigure.thymeleaf.ThymeleafAutoConfiguration;
 import org.springframework.boot.autoconfigure.validation.ValidationAutoConfiguration;
+import org.springframework.boot.autoconfigure.web.reactive.error.ErrorWebFluxAutoConfiguration;
 import org.springframework.boot.test.autoconfigure.web.reactive.WebFluxTest;
 import org.springframework.context.ApplicationContext;
 import org.springframework.test.context.junit4.SpringRunner;
@@ -37,6 +38,7 @@ import static org.springframework.boot.test.autoconfigure.AutoConfigurationImpor
  *
  * @author Stephane Nicoll
  * @author Artsiom Yudovin
+ * @author Ali Dehghani
  */
 @RunWith(SpringRunner.class)
 @WebFluxTest
@@ -75,4 +77,10 @@ public class WebFluxTestAutoConfigurationIntegrationTests {
 				.has(importedAutoConfiguration(ThymeleafAutoConfiguration.class));
 	}
 
+	@Test
+	public void errorWebFluxAutoConfigurationIsImported() {
+		assertThat(this.applicationContext)
+				.has(importedAutoConfiguration(ErrorWebFluxAutoConfiguration.class));
+	}
+
 }