Add tests for LoadBalancerHandlerConfiguration (#3779)

* Add autoconfiguration tests.

Signed-off-by: Olga Maciaszek-Sharma <olga.maciaszek-sharma@broadcom.com>

spring-cloud-gateway-server-mvc/src/test/java/org/springframework/cloud/gateway/server/mvc/GatewayServerMvcAutoConfigurationTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2013-2024 the original author or authors.
+ * Copyright 2013-2025 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.
@@ -34,6 +34,7 @@ import org.springframework.boot.builder.SpringApplicationBuilder;
 import org.springframework.boot.http.client.ClientHttpRequestFactoryBuilder;
 import org.springframework.boot.http.client.ClientHttpRequestFactorySettings;
 import org.springframework.boot.http.client.SimpleClientHttpRequestFactoryBuilder;
+import org.springframework.boot.test.context.FilteredClassLoader;
 import org.springframework.boot.test.context.runner.ApplicationContextRunner;
 import org.springframework.cloud.gateway.server.mvc.filter.FilterAutoConfiguration;
 import org.springframework.cloud.gateway.server.mvc.filter.FormFilter;
@@ -47,6 +48,7 @@ import org.springframework.cloud.gateway.server.mvc.filter.WeightCalculatorFilte
 import org.springframework.cloud.gateway.server.mvc.filter.XForwardedRequestHeadersFilter;
 import org.springframework.cloud.gateway.server.mvc.handler.HandlerFunctionAutoConfiguration;
 import org.springframework.cloud.gateway.server.mvc.predicate.PredicateAutoConfiguration;
+import org.springframework.cloud.loadbalancer.annotation.LoadBalancerClient;
 import org.springframework.context.ConfigurableApplicationContext;
 
 import static org.assertj.core.api.Assertions.assertThat;
@@ -204,6 +206,27 @@ public class GatewayServerMvcAutoConfigurationTests {
 		assertThat(builder).isInstanceOf(SimpleClientHttpRequestFactoryBuilder.class);
 	}
 
+	@Test
+	void loadBalancerFunctionHandlerAdded() {
+		new ApplicationContextRunner()
+				.withConfiguration(AutoConfigurations.of(FilterAutoConfiguration.class, PredicateAutoConfiguration.class,
+						HandlerFunctionAutoConfiguration.class, GatewayServerMvcAutoConfiguration.class,
+						HttpClientAutoConfiguration.class, RestTemplateAutoConfiguration.class,
+						RestClientAutoConfiguration.class))
+				.run(context -> assertThat(context).hasBean("lbHandlerFunctionDefinition"));
+	}
+
+	@Test
+	void loadBalancerFunctionHandlerNotAddedWhenNoLoadBalancerClientOnClasspath() {
+		new ApplicationContextRunner()
+				.withConfiguration(AutoConfigurations.of(FilterAutoConfiguration.class, PredicateAutoConfiguration.class,
+						HandlerFunctionAutoConfiguration.class, GatewayServerMvcAutoConfiguration.class,
+						HttpClientAutoConfiguration.class, RestTemplateAutoConfiguration.class,
+						RestClientAutoConfiguration.class))
+				.withClassLoader(new FilteredClassLoader(LoadBalancerClient.class))
+				.run(context -> assertThat(context).doesNotHaveBean("lbHandlerFunctionDefinition"));
+	}
+
 	@SpringBootConfiguration
 	@EnableAutoConfiguration
 	static class TestConfig {

spring-cloud-gateway-server-mvc/src/test/java/org/springframework/cloud/gateway/server/mvc/ServerMvcLoadBalancerIntegrationTests.java

@@ -0,0 +1,62 @@
+/*
+ * Copyright 2013-2025 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.cloud.gateway.server.mvc;
+
+import org.junit.jupiter.api.Test;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.boot.test.web.server.LocalServerPort;
+import org.springframework.cloud.gateway.server.mvc.filter.FilterAutoConfiguration;
+import org.springframework.cloud.gateway.server.mvc.test.HttpbinTestcontainers;
+import org.springframework.cloud.gateway.server.mvc.test.TestLoadBalancerConfig;
+import org.springframework.cloud.gateway.server.mvc.test.client.TestRestClient;
+import org.springframework.cloud.loadbalancer.annotation.LoadBalancerClient;
+import org.springframework.test.context.ActiveProfiles;
+import org.springframework.test.context.ContextConfiguration;
+
+/**
+ * Integration tests for {@link FilterAutoConfiguration.LoadBalancerHandlerConfiguration}.
+ *
+ * @author Olga Maciaszek-Sharma
+ *
+ */
+@SpringBootTest(classes = {ServerMvcLoadBalancerIntegrationTests.Config.class, FilterAutoConfiguration.class},
+		webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT)
+@ContextConfiguration(initializers = HttpbinTestcontainers.class)
+@ActiveProfiles("lb")
+public class ServerMvcLoadBalancerIntegrationTests {
+
+	@LocalServerPort
+	int port;
+
+	@Autowired
+	TestRestClient testRestClient;
+
+	@Test
+	void shouldUseLbHandlerFunctionDefinitionToResolveHost() {
+		testRestClient.get()
+				.uri("http://localhost:" + port + "/test")
+				.exchange().expectStatus().isOk();
+	}
+
+	@SpringBootApplication
+	@LoadBalancerClient(name = "httpbin", configuration = TestLoadBalancerConfig.Httpbin.class)
+	static class Config {
+	}
+}

spring-cloud-gateway-server-mvc/src/test/resources/application-lb.yml

@@ -0,0 +1,11 @@
+spring:
+  cloud:
+    gateway:
+      mvc:
+        routes:
+          - id: test
+            uri: lb://httpbin
+            predicates:
+              - Path=/test/**
+            filters:
+              - StripPrefix=1