Configure a RestClient.Builder with RestClientTest

This commit adds support for configuring a `RestClient.Builder` and
`MockRestServiceServer` support for the `RestClient` when using
`@RestClientTest` sliced tests.

Closes gh-37033

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

@@ -735,17 +735,21 @@ include::code:server/MyDataLdapTests[]
 [[features.testing.spring-boot-applications.autoconfigured-rest-client]]
 ==== Auto-configured REST Clients
 You can use the `@RestClientTest` annotation to test REST clients.
-By default, it auto-configures Jackson, GSON, and Jsonb support, configures a `RestTemplateBuilder`, and adds support for `MockRestServiceServer`.
+By default, it auto-configures Jackson, GSON, and Jsonb support, configures a `RestTemplateBuilder` and a `RestClient.Builder`, and adds support for `MockRestServiceServer`.
 Regular `@Component` and `@ConfigurationProperties` beans are not scanned when the `@RestClientTest` annotation is used.
 `@EnableConfigurationProperties` can be used to include `@ConfigurationProperties` beans.
 
 TIP: A list of the auto-configuration settings that are enabled by `@RestClientTest` can be <<test-auto-configuration#appendix.test-auto-configuration,found in the appendix>>.
 
-The specific beans that you want to test should be specified by using the `value` or `components` attribute of `@RestClientTest`, as shown in the following example:
+The specific beans that you want to test should be specified by using the `value` or `components` attribute of `@RestClientTest`.
 
-include::code:MyRestClientTests[]
+When using a `RestTemplateBuilder` in the beans under test and `RestTemplateBuilder.rootUri(String rootUri)` has been called when building the `RestTemplate`, then the root URI should be omitted from the `MockRestServiceServer` expectations as shown in the following example:
 
+include::code:MyRestTemplateServiceTests[]
 
+When using a `RestClient.Builder` in the beans under test, or when using a `RestTemplateBuilder` without calling `rootUri(String rootURI)`, the full URI must be used in the `MockRestServiceServer` expectations as shown in the following example:
+
+include::code:MyRestClientServiceTests[]
 
 [[features.testing.spring-boot-applications.autoconfigured-spring-restdocs]]
 ==== Auto-configured Spring REST Docs Tests

spring-boot-project/spring-boot-docs/src/main/java/org/springframework/boot/docs/features/testing/springbootapplications/autoconfiguredrestclient/MyRestClientServiceTests.java

@@ -0,0 +1,47 @@
+/*
+ * Copyright 2012-2023 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.boot.docs.features.testing.springbootapplications.autoconfiguredrestclient;
+
+import org.junit.jupiter.api.Test;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.autoconfigure.web.client.RestClientTest;
+import org.springframework.http.MediaType;
+import org.springframework.test.web.client.MockRestServiceServer;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.springframework.test.web.client.match.MockRestRequestMatchers.requestTo;
+import static org.springframework.test.web.client.response.MockRestResponseCreators.withSuccess;
+
+@RestClientTest(RemoteVehicleDetailsService.class)
+class MyRestClientServiceTests {
+
+	@Autowired
+	private RemoteVehicleDetailsService service;
+
+	@Autowired
+	private MockRestServiceServer server;
+
+	@Test
+	void getVehicleDetailsWhenResultIsSuccessShouldReturnDetails() {
+		this.server.expect(requestTo("https://example.com/greet/details"))
+			.andRespond(withSuccess("hello", MediaType.TEXT_PLAIN));
+		String greeting = this.service.callRestService();
+		assertThat(greeting).isEqualTo("hello");
+	}
+
+}

spring-boot-project/spring-boot-docs/src/main/java/org/springframework/boot/docs/features/testing/springbootapplications/autoconfiguredrestclient/MyRestTemplateServiceTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2022 the original author or authors.
+ * Copyright 2012-2023 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.
@@ -28,7 +28,7 @@ import static org.springframework.test.web.client.match.MockRestRequestMatchers.
 import static org.springframework.test.web.client.response.MockRestResponseCreators.withSuccess;
 
 @RestClientTest(RemoteVehicleDetailsService.class)
-class MyRestClientTests {
+class MyRestTemplateServiceTests {
 
 	@Autowired
 	private RemoteVehicleDetailsService service;

spring-boot-project/spring-boot-docs/src/main/kotlin/org/springframework/boot/docs/features/testing/springbootapplications/autoconfiguredrestclient/MyRestClientServiceTests.kt

@@ -0,0 +1,41 @@
+/*
+ * Copyright 2012-2023 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.boot.docs.features.testing.springbootapplications.autoconfiguredrestclient
+
+import org.assertj.core.api.Assertions.assertThat
+import org.junit.jupiter.api.Test
+import org.springframework.beans.factory.annotation.Autowired
+import org.springframework.boot.test.autoconfigure.web.client.RestClientTest
+import org.springframework.http.MediaType
+import org.springframework.test.web.client.MockRestServiceServer
+import org.springframework.test.web.client.match.MockRestRequestMatchers
+import org.springframework.test.web.client.response.MockRestResponseCreators
+
+@RestClientTest(RemoteVehicleDetailsService::class)
+class MyRestClientServiceTests(
+	@Autowired val service: RemoteVehicleDetailsService,
+	@Autowired val server: MockRestServiceServer) {
+
+	@Test
+	fun getVehicleDetailsWhenResultIsSuccessShouldReturnDetails(): Unit {
+		server.expect(MockRestRequestMatchers.requestTo("https://example.com/greet/details"))
+			.andRespond(MockRestResponseCreators.withSuccess("hello", MediaType.TEXT_PLAIN))
+		val greeting = service.callRestService()
+		assertThat(greeting).isEqualTo("hello")
+	}
+
+}

spring-boot-project/spring-boot-docs/src/main/kotlin/org/springframework/boot/docs/features/testing/springbootapplications/autoconfiguredrestclient/MyRestTemplateServiceTests.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2022 the original author or authors.
+ * Copyright 2012-2023 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.
@@ -26,7 +26,7 @@ import org.springframework.test.web.client.match.MockRestRequestMatchers
 import org.springframework.test.web.client.response.MockRestResponseCreators
 
 @RestClientTest(RemoteVehicleDetailsService::class)
-class MyRestClientTests(
+class MyRestTemplateServiceTests(
 	@Autowired val service: RemoteVehicleDetailsService,
 	@Autowired val server: MockRestServiceServer) {
 

spring-boot-project/spring-boot-test-autoconfigure/src/main/java/org/springframework/boot/test/autoconfigure/web/client/AutoConfigureMockRestServiceServer.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2019 the original author or authors.
+ * Copyright 2012-2023 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.
@@ -25,20 +25,26 @@ import java.lang.annotation.Target;
 
 import org.springframework.boot.autoconfigure.ImportAutoConfiguration;
 import org.springframework.boot.test.autoconfigure.properties.PropertyMapping;
+import org.springframework.boot.test.web.client.MockServerRestClientCustomizer;
 import org.springframework.boot.test.web.client.MockServerRestTemplateCustomizer;
 import org.springframework.boot.web.client.RestTemplateBuilder;
 import org.springframework.test.web.client.MockRestServiceServer;
+import org.springframework.web.client.RestClient;
 
 /**
  * Annotation that can be applied to a test class to enable and configure
  * auto-configuration of a single {@link MockRestServiceServer}. Only useful when a single
- * call is made to {@link RestTemplateBuilder}. If multiple
+ * call is made to {@link RestTemplateBuilder} or {@link RestClient.Builder}. If multiple
- * {@link org.springframework.web.client.RestTemplate RestTemplates} are in use, inject
+ * {@link org.springframework.web.client.RestTemplate RestTemplates} or
+ * {@link org.springframework.web.client.RestClient RestClients} are in use, inject a
  * {@link MockServerRestTemplateCustomizer} and use
  * {@link MockServerRestTemplateCustomizer#getServer(org.springframework.web.client.RestTemplate)
- * getServer(RestTemplate)} or bind a {@link MockRestServiceServer} directly.
+ * getServer(RestTemplate)}, or inject a {@link MockServerRestClientCustomizer} and use
+ * {@link MockServerRestClientCustomizer#getServer(org.springframework.web.client.RestClient.Builder)
+ * * getServer(RestClient.Builder)}, or bind a {@link MockRestServiceServer} directly.
  *
  * @author Phillip Webb
+ * @author Scott Frederick
  * @since 1.4.0
  * @see MockServerRestTemplateCustomizer
  */
@@ -51,7 +57,8 @@ import org.springframework.test.web.client.MockRestServiceServer;
 public @interface AutoConfigureMockRestServiceServer {
 
 	/**
-	 * If {@link MockServerRestTemplateCustomizer} should be enabled and
+	 * If {@link MockServerRestTemplateCustomizer} and
+	 * {@link MockServerRestClientCustomizer} should be enabled and
 	 * {@link MockRestServiceServer} beans should be registered. Defaults to {@code true}
 	 * @return if mock support is enabled
 	 */

spring-boot-project/spring-boot-test-autoconfigure/src/main/java/org/springframework/boot/test/autoconfigure/web/client/MockRestServiceServerAutoConfiguration.java

@@ -19,10 +19,12 @@ package org.springframework.boot.test.autoconfigure.web.client;
 import java.io.IOException;
 import java.lang.reflect.Constructor;
 import java.time.Duration;
+import java.util.Collection;
 import java.util.Map;
 
 import org.springframework.boot.autoconfigure.AutoConfiguration;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
+import org.springframework.boot.test.web.client.MockServerRestClientCustomizer;
 import org.springframework.boot.test.web.client.MockServerRestTemplateCustomizer;
 import org.springframework.context.annotation.Bean;
 import org.springframework.http.client.ClientHttpRequest;
@@ -33,12 +35,14 @@ import org.springframework.test.web.client.RequestExpectationManager;
 import org.springframework.test.web.client.RequestMatcher;
 import org.springframework.test.web.client.ResponseActions;
 import org.springframework.util.Assert;
+import org.springframework.web.client.RestClient;
 import org.springframework.web.client.RestTemplate;
 
 /**
  * Auto-configuration for {@link MockRestServiceServer} support.
  *
  * @author Phillip Webb
+ * @author Scott Frederick
  * @since 1.4.0
  * @see AutoConfigureMockRestServiceServer
  */
@@ -52,21 +56,29 @@ public class MockRestServiceServerAutoConfiguration {
 	}
 
 	@Bean
-	public MockRestServiceServer mockRestServiceServer(MockServerRestTemplateCustomizer customizer) {
+	public MockServerRestClientCustomizer mockServerRestClientCustomizer() {
+		return new MockServerRestClientCustomizer();
+	}
+
+	@Bean
+	public MockRestServiceServer mockRestServiceServer(MockServerRestTemplateCustomizer restTemplateCustomizer,
+			MockServerRestClientCustomizer restClientCustomizer) {
 		try {
-			return createDeferredMockRestServiceServer(customizer);
+			return createDeferredMockRestServiceServer(restTemplateCustomizer, restClientCustomizer);
 		}
 		catch (Exception ex) {
 			throw new IllegalStateException(ex);
 		}
 	}
 
-	private MockRestServiceServer createDeferredMockRestServiceServer(MockServerRestTemplateCustomizer customizer)
+	private MockRestServiceServer createDeferredMockRestServiceServer(
-			throws Exception {
+			MockServerRestTemplateCustomizer restTemplateCustomizer,
+			MockServerRestClientCustomizer restClientCustomizer) throws Exception {
 		Constructor<MockRestServiceServer> constructor = MockRestServiceServer.class
 			.getDeclaredConstructor(RequestExpectationManager.class);
 		constructor.setAccessible(true);
-		return constructor.newInstance(new DeferredRequestExpectationManager(customizer));
+		return constructor
+			.newInstance(new DeferredRequestExpectationManager(restTemplateCustomizer, restClientCustomizer));
 	}
 
 	/**
@@ -77,10 +89,14 @@ public class MockRestServiceServerAutoConfiguration {
 	 */
 	private static class DeferredRequestExpectationManager implements RequestExpectationManager {
 
-		private final MockServerRestTemplateCustomizer customizer;
+		private final MockServerRestTemplateCustomizer restTemplateCustomizer;
+
+		private final MockServerRestClientCustomizer restClientCustomizer;
 
-		DeferredRequestExpectationManager(MockServerRestTemplateCustomizer customizer) {
+		DeferredRequestExpectationManager(MockServerRestTemplateCustomizer restTemplateCustomizer,
-			this.customizer = customizer;
+				MockServerRestClientCustomizer restClientCustomizer) {
+			this.restTemplateCustomizer = restTemplateCustomizer;
+			this.restClientCustomizer = restClientCustomizer;
 		}
 
 		@Override
@@ -105,19 +121,34 @@ public class MockRestServiceServerAutoConfiguration {
 
 		@Override
 		public void reset() {
-			Map<RestTemplate, RequestExpectationManager> expectationManagers = this.customizer.getExpectationManagers();
+			resetExpectations(this.restTemplateCustomizer.getExpectationManagers().values());
+			resetExpectations(this.restClientCustomizer.getExpectationManagers().values());
+		}
+
+		private void resetExpectations(Collection<RequestExpectationManager> expectationManagers) {
 			if (expectationManagers.size() == 1) {
-				getDelegate().reset();
+				expectationManagers.iterator().next().reset();
 			}
 		}
 
 		private RequestExpectationManager getDelegate() {
-			Map<RestTemplate, RequestExpectationManager> expectationManagers = this.customizer.getExpectationManagers();
+			Map<RestTemplate, RequestExpectationManager> restTemplateExpectationManagers = this.restTemplateCustomizer
-			Assert.state(!expectationManagers.isEmpty(), "Unable to use auto-configured MockRestServiceServer since "
+				.getExpectationManagers();
-					+ "MockServerRestTemplateCustomizer has not been bound to a RestTemplate");
+			Map<RestClient.Builder, RequestExpectationManager> restClientExpectationManagers = this.restClientCustomizer
-			Assert.state(expectationManagers.size() == 1, "Unable to use auto-configured MockRestServiceServer since "
+				.getExpectationManagers();
-					+ "MockServerRestTemplateCustomizer has been bound to more than one RestTemplate");
+			Assert.state(!(restTemplateExpectationManagers.isEmpty() && restClientExpectationManagers.isEmpty()),
-			return expectationManagers.values().iterator().next();
+					"Unable to use auto-configured MockRestServiceServer since "
+							+ "a mock server customizer has not been bound to a RestTemplate or RestClient");
+			if (!restTemplateExpectationManagers.isEmpty()) {
+				Assert.state(restTemplateExpectationManagers.size() == 1,
+						"Unable to use auto-configured MockRestServiceServer since "
+								+ "MockServerRestTemplateCustomizer has been bound to more than one RestTemplate");
+				return restTemplateExpectationManagers.values().iterator().next();
+			}
+			Assert.state(restClientExpectationManagers.size() == 1,
+					"Unable to use auto-configured MockRestServiceServer since "
+							+ "MockServerRestClientCustomizer has been bound to more than one RestClient");
+			return restClientExpectationManagers.values().iterator().next();
 		}
 
 	}

spring-boot-project/spring-boot-test-autoconfigure/src/main/java/org/springframework/boot/test/autoconfigure/web/client/RestClientTest.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2019 the original author or authors.
+ * Copyright 2012-2023 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.
@@ -38,11 +38,12 @@ import org.springframework.stereotype.Component;
 import org.springframework.test.context.BootstrapWith;
 import org.springframework.test.context.junit.jupiter.SpringExtension;
 import org.springframework.test.web.client.MockRestServiceServer;
+import org.springframework.web.client.RestClient;
 import org.springframework.web.client.RestTemplate;
 
 /**
  * Annotation for a Spring rest client test that focuses <strong>only</strong> on beans
- * that use {@link RestTemplateBuilder}.
+ * that use {@link RestTemplateBuilder} or {@link RestClient.Builder}.
  * <p>
  * Using this annotation will disable full auto-configuration and instead apply only
  * configuration relevant to rest client tests (i.e. Jackson or GSON auto-configuration

spring-boot-project/spring-boot-test-autoconfigure/src/main/resources/META-INF/spring/org.springframework.boot.test.autoconfigure.web.client.AutoConfigureWebClient.imports

@@ -6,4 +6,5 @@ org.springframework.boot.autoconfigure.http.codec.CodecsAutoConfiguration
 org.springframework.boot.autoconfigure.jackson.JacksonAutoConfiguration
 org.springframework.boot.autoconfigure.jsonb.JsonbAutoConfiguration
 org.springframework.boot.autoconfigure.web.client.RestTemplateAutoConfiguration
+org.springframework.boot.autoconfigure.web.client.RestClientAutoConfiguration
 org.springframework.boot.autoconfigure.web.reactive.function.client.WebClientAutoConfiguration

spring-boot-project/spring-boot-test-autoconfigure/src/test/java/org/springframework/boot/test/autoconfigure/web/client/AnotherExampleRestClientService.java

@@ -0,0 +1,48 @@
+/*
+ * Copyright 2012-2023 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.boot.test.autoconfigure.web.client;
+
+import org.springframework.stereotype.Service;
+import org.springframework.web.client.RestClient;
+import org.springframework.web.client.RestClient.Builder;
+
+/**
+ * A second example web client used with {@link RestClientTest @RestClientTest} tests.
+ *
+ * @author Scott Frederick
+ */
+@Service
+public class AnotherExampleRestClientService {
+
+	private final Builder builder;
+
+	private final RestClient restClient;
+
+	public AnotherExampleRestClientService(RestClient.Builder builder) {
+		this.builder = builder;
+		this.restClient = builder.baseUrl("https://example.com").build();
+	}
+
+	protected Builder getRestClientBuilder() {
+		return this.builder;
+	}
+
+	public String test() {
+		return this.restClient.get().uri("/test").retrieve().toEntity(String.class).getBody();
+	}
+
+}

spring-boot-project/spring-boot-test-autoconfigure/src/test/java/org/springframework/boot/test/autoconfigure/web/client/AnotherExampleRestTemplateService.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2020 the original author or authors.
+ * Copyright 2012-2023 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.
@@ -26,11 +26,11 @@ import org.springframework.web.client.RestTemplate;
  * @author Phillip Webb
  */
 @Service
-public class AnotherExampleRestClient {
+public class AnotherExampleRestTemplateService {
 
 	private final RestTemplate restTemplate;
 
-	public AnotherExampleRestClient(RestTemplateBuilder builder) {
+	public AnotherExampleRestTemplateService(RestTemplateBuilder builder) {
 		this.restTemplate = builder.rootUri("https://example.com").build();
 	}
 

spring-boot-project/spring-boot-test-autoconfigure/src/test/java/org/springframework/boot/test/autoconfigure/web/client/AutoConfigureMockRestServiceServerEnabledFalseIntegrationTests.java

@@ -20,6 +20,7 @@ import org.junit.jupiter.api.Test;
 
 import org.springframework.beans.factory.NoSuchBeanDefinitionException;
 import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.web.client.MockServerRestClientCustomizer;
 import org.springframework.boot.test.web.client.MockServerRestTemplateCustomizer;
 import org.springframework.context.ApplicationContext;
 
@@ -43,6 +44,8 @@ class AutoConfigureMockRestServiceServerEnabledFalseIntegrationTests {
 	void mockServerRestTemplateCustomizerShouldNotBeRegistered() {
 		assertThatExceptionOfType(NoSuchBeanDefinitionException.class)
 			.isThrownBy(() -> this.applicationContext.getBean(MockServerRestTemplateCustomizer.class));
+		assertThatExceptionOfType(NoSuchBeanDefinitionException.class)
+			.isThrownBy(() -> this.applicationContext.getBean(MockServerRestClientCustomizer.class));
 	}
 
 }

spring-boot-project/spring-boot-test-autoconfigure/src/test/java/org/springframework/boot/test/autoconfigure/web/client/AutoConfigureMockRestServiceServerWithRestClientIntegrationTests.java

@@ -0,0 +1,72 @@
+/*
+ * Copyright 2012-2023 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.boot.test.autoconfigure.web.client;
+
+import org.junit.jupiter.api.Test;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
+import org.springframework.boot.autoconfigure.cassandra.CassandraAutoConfiguration;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.http.MediaType;
+import org.springframework.http.ResponseEntity;
+import org.springframework.test.web.client.MockRestServiceServer;
+import org.springframework.web.client.RestClient;
+import org.springframework.web.client.RestClient.Builder;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.springframework.test.web.client.match.MockRestRequestMatchers.requestTo;
+import static org.springframework.test.web.client.response.MockRestResponseCreators.withSuccess;
+
+/**
+ * Tests for
+ * {@link AutoConfigureMockRestServiceServer @AutoConfigureMockRestServiceServer} with a
+ * {@link RestClient} configured with a base URL.
+ *
+ * @author Scott Frederick
+ */
+@SpringBootTest
+@AutoConfigureMockRestServiceServer
+class AutoConfigureMockRestServiceServerWithRestClientIntegrationTests {
+
+	@Autowired
+	private RestClient restClient;
+
+	@Autowired
+	private MockRestServiceServer server;
+
+	@Test
+	void mockServerExpectationsAreMatched() {
+		this.server.expect(requestTo("/rest/test")).andRespond(withSuccess("hello", MediaType.TEXT_HTML));
+		ResponseEntity<String> entity = this.restClient.get().uri("/test").retrieve().toEntity(String.class);
+		assertThat(entity.getBody()).isEqualTo("hello");
+	}
+
+	@EnableAutoConfiguration(exclude = CassandraAutoConfiguration.class)
+	@Configuration(proxyBeanMethods = false)
+	static class RootUriConfiguration {
+
+		@Bean
+		RestClient restClient(Builder restClientBuilder) {
+			return restClientBuilder.baseUrl("/rest").build();
+		}
+
+	}
+
+}

spring-boot-project/spring-boot-test-autoconfigure/src/test/java/org/springframework/boot/test/autoconfigure/web/client/AutoConfigureMockRestServiceServerWithRestTemplateRootUriIntegrationTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2022 the original author or authors.
+ * Copyright 2012-2023 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.
@@ -44,7 +44,7 @@ import static org.springframework.test.web.client.response.MockRestResponseCreat
  */
 @SpringBootTest
 @AutoConfigureMockRestServiceServer
-class AutoConfigureMockRestServiceServerWithRootUriIntegrationTests {
+class AutoConfigureMockRestServiceServerWithRestTemplateRootUriIntegrationTests {
 
 	@Autowired
 	private RestTemplate restTemplate;

spring-boot-project/spring-boot-test-autoconfigure/src/test/java/org/springframework/boot/test/autoconfigure/web/client/ExampleRestClientService.java

@@ -0,0 +1,53 @@
+/*
+ * Copyright 2012-2023 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.boot.test.autoconfigure.web.client;
+
+import org.springframework.stereotype.Service;
+import org.springframework.web.client.RestClient;
+import org.springframework.web.client.RestClient.Builder;
+
+/**
+ * Example web client using {@code RestClient} with {@link RestClientTest @RestClientTest}
+ * tests.
+ *
+ * @author Scott Frederick
+ */
+@Service
+public class ExampleRestClientService {
+
+	private final Builder builder;
+
+	private final RestClient restClient;
+
+	public ExampleRestClientService(RestClient.Builder builder) {
+		this.builder = builder;
+		this.restClient = builder.baseUrl("https://example.com").build();
+	}
+
+	protected Builder getRestClientBuilder() {
+		return this.builder;
+	}
+
+	public String test() {
+		return this.restClient.get().uri("/test").retrieve().toEntity(String.class).getBody();
+	}
+
+	public void testPostWithBody(String body) {
+		this.restClient.post().uri("/test").body(body).retrieve().toBodilessEntity();
+	}
+
+}

spring-boot-project/spring-boot-test-autoconfigure/src/test/java/org/springframework/boot/test/autoconfigure/web/client/ExampleRestTemplateService.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2022 the original author or authors.
+ * Copyright 2012-2023 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.
@@ -21,16 +21,17 @@ import org.springframework.stereotype.Service;
 import org.springframework.web.client.RestTemplate;
 
 /**
- * Example web client used with {@link RestClientTest @RestClientTest} tests.
+ * Example web client using {@code RestTemplate} with
+ * {@link RestClientTest @RestClientTest} tests.
  *
  * @author Phillip Webb
  */
 @Service
-public class ExampleRestClient {
+public class ExampleRestTemplateService {
 
 	private final RestTemplate restTemplate;
 
-	public ExampleRestClient(RestTemplateBuilder builder) {
+	public ExampleRestTemplateService(RestTemplateBuilder builder) {
 		this.restTemplate = builder.rootUri("https://example.com").build();
 	}
 

spring-boot-project/spring-boot-test-autoconfigure/src/test/java/org/springframework/boot/test/autoconfigure/web/client/RestClientTestNoComponentIntegrationTests.java

@@ -50,7 +50,7 @@ class RestClientTestNoComponentIntegrationTests {
 	@Test
 	void exampleRestClientIsNotInjected() {
 		assertThatExceptionOfType(NoSuchBeanDefinitionException.class)
-			.isThrownBy(() -> this.applicationContext.getBean(ExampleRestClient.class));
+			.isThrownBy(() -> this.applicationContext.getBean(ExampleRestTemplateService.class));
 	}
 
 	@Test
@@ -61,7 +61,7 @@ class RestClientTestNoComponentIntegrationTests {
 
 	@Test
 	void manuallyCreateBean() {
-		ExampleRestClient client = new ExampleRestClient(this.restTemplateBuilder);
+		ExampleRestTemplateService client = new ExampleRestTemplateService(this.restTemplateBuilder);
 		this.server.expect(requestTo("/test")).andRespond(withSuccess("hello", MediaType.TEXT_HTML));
 		assertThat(client.test()).isEqualTo("hello");
 	}

spring-boot-project/spring-boot-test-autoconfigure/src/test/java/org/springframework/boot/test/autoconfigure/web/client/RestClientTestRestClientIntegrationTests.java

@@ -0,0 +1,69 @@
+/*
+ * Copyright 2012-2023 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.boot.test.autoconfigure.web.client;
+
+import org.junit.jupiter.api.Test;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.http.MediaType;
+import org.springframework.test.web.client.MockRestServiceServer;
+import org.springframework.web.client.RestClient;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.springframework.test.web.client.match.MockRestRequestMatchers.content;
+import static org.springframework.test.web.client.match.MockRestRequestMatchers.requestTo;
+import static org.springframework.test.web.client.response.MockRestResponseCreators.withSuccess;
+
+/**
+ * Tests for {@link RestClientTest @RestClientTest} with a {@link RestClient}.
+ *
+ * @author Scott Frederick
+ */
+@RestClientTest(ExampleRestClientService.class)
+class RestClientTestRestClientIntegrationTests {
+
+	@Autowired
+	private MockRestServiceServer server;
+
+	@Autowired
+	private ExampleRestClientService client;
+
+	@Test
+	void mockServerCall1() {
+		this.server.expect(requestTo(uri("/test"))).andRespond(withSuccess("1", MediaType.TEXT_HTML));
+		assertThat(this.client.test()).isEqualTo("1");
+	}
+
+	@Test
+	void mockServerCall2() {
+		this.server.expect(requestTo(uri("/test"))).andRespond(withSuccess("2", MediaType.TEXT_HTML));
+		assertThat(this.client.test()).isEqualTo("2");
+	}
+
+	@Test
+	void mockServerCallWithContent() {
+		this.server.expect(requestTo(uri("/test")))
+			.andExpect(content().string("test"))
+			.andRespond(withSuccess("1", MediaType.TEXT_HTML));
+		this.client.testPostWithBody("test");
+	}
+
+	private static String uri(String path) {
+		return "https://example.com" + path;
+	}
+
+}

spring-boot-project/spring-boot-test-autoconfigure/src/test/java/org/springframework/boot/test/autoconfigure/web/client/RestClientTestRestClientTwoComponentsIntegrationTests.java

@@ -0,0 +1,79 @@
+/*
+ * Copyright 2012-2023 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.boot.test.autoconfigure.web.client;
+
+import org.junit.jupiter.api.Test;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.web.client.MockServerRestClientCustomizer;
+import org.springframework.http.MediaType;
+import org.springframework.test.web.client.MockRestServiceServer;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatIllegalStateException;
+import static org.springframework.test.web.client.match.MockRestRequestMatchers.requestTo;
+import static org.springframework.test.web.client.response.MockRestResponseCreators.withSuccess;
+
+/**
+ * Tests for {@link RestClientTest @RestClientTest} with two {@code RestClient} clients.
+ *
+ * @author Phillip Webb
+ * @author Scott Frederick
+ */
+@RestClientTest({ ExampleRestClientService.class, AnotherExampleRestClientService.class })
+class RestClientTestRestClientTwoComponentsIntegrationTests {
+
+	@Autowired
+	private ExampleRestClientService client1;
+
+	@Autowired
+	private AnotherExampleRestClientService client2;
+
+	@Autowired
+	private MockServerRestClientCustomizer customizer;
+
+	@Autowired
+	private MockRestServiceServer server;
+
+	@Test
+	void serverShouldNotWork() {
+		assertThatIllegalStateException().isThrownBy(
+				() -> this.server.expect(requestTo(uri("/test"))).andRespond(withSuccess("hello", MediaType.TEXT_HTML)))
+			.withMessageContaining("Unable to use auto-configured");
+	}
+
+	@Test
+	void client1RestCallViaCustomizer() {
+		this.customizer.getServer(this.client1.getRestClientBuilder())
+			.expect(requestTo(uri("/test")))
+			.andRespond(withSuccess("hello", MediaType.TEXT_HTML));
+		assertThat(this.client1.test()).isEqualTo("hello");
+	}
+
+	@Test
+	void client2RestCallViaCustomizer() {
+		this.customizer.getServer(this.client2.getRestClientBuilder())
+			.expect(requestTo(uri("/test")))
+			.andRespond(withSuccess("there", MediaType.TEXT_HTML));
+		assertThat(this.client2.test()).isEqualTo("there");
+	}
+
+	private static String uri(String path) {
+		return "https://example.com" + path;
+	}
+
+}

spring-boot-project/spring-boot-test-autoconfigure/src/test/java/org/springframework/boot/test/autoconfigure/web/client/RestClientTestRestTemplateIntegrationTests.java

@@ -32,14 +32,14 @@ import static org.springframework.test.web.client.response.MockRestResponseCreat
  *
  * @author Phillip Webb
  */
-@RestClientTest(ExampleRestClient.class)
+@RestClientTest(ExampleRestTemplateService.class)
-class RestClientRestIntegrationTests {
+class RestClientTestRestTemplateIntegrationTests {
 
 	@Autowired
 	private MockRestServiceServer server;
 
 	@Autowired
-	private ExampleRestClient client;
+	private ExampleRestTemplateService client;
 
 	@Test
 	void mockServerCall1() {

spring-boot-project/spring-boot-test-autoconfigure/src/test/java/org/springframework/boot/test/autoconfigure/web/client/RestClientTestRestTemplateTwoComponentsIntegrationTests.java

@@ -29,18 +29,18 @@ import static org.springframework.test.web.client.match.MockRestRequestMatchers.
 import static org.springframework.test.web.client.response.MockRestResponseCreators.withSuccess;
 
 /**
- * Tests for {@link RestClientTest @RestClientTest} with two clients.
+ * Tests for {@link RestClientTest @RestClientTest} with two {@code RestTemplate} clients.
  *
  * @author Phillip Webb
  */
-@RestClientTest({ ExampleRestClient.class, AnotherExampleRestClient.class })
+@RestClientTest({ ExampleRestTemplateService.class, AnotherExampleRestTemplateService.class })
-class RestClientTestTwoComponentsIntegrationTests {
+class RestClientTestRestTemplateTwoComponentsIntegrationTests {
 
 	@Autowired
-	private ExampleRestClient client1;
+	private ExampleRestTemplateService client1;
 
 	@Autowired
-	private AnotherExampleRestClient client2;
+	private AnotherExampleRestTemplateService client2;
 
 	@Autowired
 	private MockServerRestTemplateCustomizer customizer;

spring-boot-project/spring-boot-test-autoconfigure/src/test/java/org/springframework/boot/test/autoconfigure/web/client/RestClientTestWithRestClientComponentIntegrationTests.java

@@ -0,0 +1,51 @@
+/*
+ * Copyright 2012-2023 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.boot.test.autoconfigure.web.client;
+
+import org.junit.jupiter.api.Test;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.http.MediaType;
+import org.springframework.test.web.client.MockRestServiceServer;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.springframework.test.web.client.match.MockRestRequestMatchers.requestTo;
+import static org.springframework.test.web.client.response.MockRestResponseCreators.withSuccess;
+
+/**
+ * Tests for {@link RestClientTest @RestClientTest} with a single client using
+ * {@code RestClient}.
+ *
+ * @author Phillip Webb
+ * @author Scott Frederick
+ */
+@RestClientTest(ExampleRestClientService.class)
+class RestClientTestWithRestClientComponentIntegrationTests {
+
+	@Autowired
+	private MockRestServiceServer server;
+
+	@Autowired
+	private ExampleRestClientService client;
+
+	@Test
+	void mockServerCall() {
+		this.server.expect(requestTo("https://example.com/test")).andRespond(withSuccess("hello", MediaType.TEXT_HTML));
+		assertThat(this.client.test()).isEqualTo("hello");
+	}
+
+}

spring-boot-project/spring-boot-test-autoconfigure/src/test/java/org/springframework/boot/test/autoconfigure/web/client/RestClientTestWithRestTemplateComponentIntegrationTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2019 the original author or authors.
+ * Copyright 2012-2023 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.
@@ -27,18 +27,19 @@ import static org.springframework.test.web.client.match.MockRestRequestMatchers.
 import static org.springframework.test.web.client.response.MockRestResponseCreators.withSuccess;
 
 /**
- * Tests for {@link RestClientTest @RestClientTest} with a single client.
+ * Tests for {@link RestClientTest @RestClientTest} with a single client using
+ * {@code RestTemplate}.
  *
  * @author Phillip Webb
  */
-@RestClientTest(ExampleRestClient.class)
+@RestClientTest(ExampleRestTemplateService.class)
-class RestClientTestWithComponentIntegrationTests {
+class RestClientTestWithRestTemplateComponentIntegrationTests {
 
 	@Autowired
 	private MockRestServiceServer server;
 
 	@Autowired
-	private ExampleRestClient client;
+	private ExampleRestTemplateService client;
 
 	@Test
 	void mockServerCall() {

spring-boot-project/spring-boot-test-autoconfigure/src/test/java/org/springframework/boot/test/autoconfigure/web/client/RestClientTestWithoutJacksonIntegrationTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2019 the original author or authors.
+ * Copyright 2012-2023 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.
@@ -34,14 +34,14 @@ import static org.springframework.test.web.client.response.MockRestResponseCreat
  * @author Andy Wilkinson
  */
 @ClassPathExclusions("jackson-*.jar")
-@RestClientTest(ExampleRestClient.class)
+@RestClientTest(ExampleRestTemplateService.class)
 class RestClientTestWithoutJacksonIntegrationTests {
 
 	@Autowired
 	private MockRestServiceServer server;
 
 	@Autowired
-	private ExampleRestClient client;
+	private ExampleRestTemplateService client;
 
 	@Test
 	void restClientTestCanBeUsedWhenJacksonIsNotOnTheClassPath() {

spring-boot-project/spring-boot-test/src/main/java/org/springframework/boot/test/web/client/MockServerRestClientCustomizer.java

@@ -0,0 +1,139 @@
+/*
+ * Copyright 2012-2023 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.boot.test.web.client;
+
+import java.util.Collections;
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.function.Supplier;
+
+import org.springframework.beans.BeanUtils;
+import org.springframework.boot.web.client.RestClientCustomizer;
+import org.springframework.http.client.BufferingClientHttpRequestFactory;
+import org.springframework.test.web.client.MockRestServiceServer;
+import org.springframework.test.web.client.MockRestServiceServer.MockRestServiceServerBuilder;
+import org.springframework.test.web.client.RequestExpectationManager;
+import org.springframework.test.web.client.SimpleRequestExpectationManager;
+import org.springframework.util.Assert;
+import org.springframework.web.client.RestClient;
+
+/**
+ * {@link RestClientCustomizer} that can be applied to {@link RestClient.Builder}
+ * instances to add {@link MockRestServiceServer} support.
+ * <p>
+ * Typically applied to an existing builder before it is used, for example:
+ * <pre class="code">
+ * MockServerRestClientCustomizer customizer = new MockServerRestClientCustomizer();
+ * RestClient.Builder builder = RestClient.builder();
+ * customizer.customize(builder);
+ * MyBean bean = new MyBean(client.build());
+ * customizer.getServer().expect(requestTo("/hello")).andRespond(withSuccess());
+ * bean.makeRestCall();
+ * </pre>
+ * <p>
+ * If the customizer is only used once, the {@link #getServer()} method can be used to
+ * obtain the mock server. If the customizer has been used more than once the
+ * {@link #getServer(RestClient.Builder)} or {@link #getServers()} method must be used to
+ * access the related server.
+ *
+ * @author Scott Frederick
+ * @since 3.2.0
+ * @see #getServer()
+ * @see #getServer(RestClient.Builder)
+ */
+public class MockServerRestClientCustomizer implements RestClientCustomizer {
+
+	private final Map<RestClient.Builder, RequestExpectationManager> expectationManagers = new ConcurrentHashMap<>();
+
+	private final Map<RestClient.Builder, MockRestServiceServer> servers = new ConcurrentHashMap<>();
+
+	private final Supplier<? extends RequestExpectationManager> expectationManagerSupplier;
+
+	private boolean bufferContent = false;
+
+	public MockServerRestClientCustomizer() {
+		this(SimpleRequestExpectationManager::new);
+	}
+
+	/**
+	 * Crate a new {@link MockServerRestClientCustomizer} instance.
+	 * @param expectationManager the expectation manager class to use
+	 */
+	public MockServerRestClientCustomizer(Class<? extends RequestExpectationManager> expectationManager) {
+		this(() -> BeanUtils.instantiateClass(expectationManager));
+		Assert.notNull(expectationManager, "ExpectationManager must not be null");
+	}
+
+	/**
+	 * Crate a new {@link MockServerRestClientCustomizer} instance.
+	 * @param expectationManagerSupplier a supplier that provides the
+	 * {@link RequestExpectationManager} to use
+	 * @since 3.0.0
+	 */
+	public MockServerRestClientCustomizer(Supplier<? extends RequestExpectationManager> expectationManagerSupplier) {
+		Assert.notNull(expectationManagerSupplier, "ExpectationManagerSupplier must not be null");
+		this.expectationManagerSupplier = expectationManagerSupplier;
+	}
+
+	/**
+	 * Set if the {@link BufferingClientHttpRequestFactory} wrapper should be used to
+	 * buffer the input and output streams, and for example, allow multiple reads of the
+	 * response body.
+	 * @param bufferContent if request and response content should be buffered
+	 * @since 3.1.0
+	 */
+	public void setBufferContent(boolean bufferContent) {
+		this.bufferContent = bufferContent;
+	}
+
+	@Override
+	public void customize(RestClient.Builder restClientBuilder) {
+		RequestExpectationManager expectationManager = createExpectationManager();
+		MockRestServiceServerBuilder serverBuilder = MockRestServiceServer.bindTo(restClientBuilder);
+		if (this.bufferContent) {
+			serverBuilder.bufferContent();
+		}
+		MockRestServiceServer server = serverBuilder.build(expectationManager);
+		this.expectationManagers.put(restClientBuilder, expectationManager);
+		this.servers.put(restClientBuilder, server);
+	}
+
+	protected RequestExpectationManager createExpectationManager() {
+		return this.expectationManagerSupplier.get();
+	}
+
+	public MockRestServiceServer getServer() {
+		Assert.state(!this.servers.isEmpty(), "Unable to return a single MockRestServiceServer since "
+				+ "MockServerRestClientCustomizer has not been bound to a RestClient");
+		Assert.state(this.servers.size() == 1, "Unable to return a single MockRestServiceServer since "
+				+ "MockServerRestClientCustomizer has been bound to more than one RestClient");
+		return this.servers.values().iterator().next();
+	}
+
+	public Map<RestClient.Builder, RequestExpectationManager> getExpectationManagers() {
+		return this.expectationManagers;
+	}
+
+	public MockRestServiceServer getServer(RestClient.Builder restClientBuilder) {
+		return this.servers.get(restClientBuilder);
+	}
+
+	public Map<RestClient.Builder, MockRestServiceServer> getServers() {
+		return Collections.unmodifiableMap(this.servers);
+	}
+
+}

spring-boot-project/spring-boot-test/src/test/java/org/springframework/boot/test/web/client/MockServerRestClientCustomizerTests.java

@@ -0,0 +1,163 @@
+/*
+ * Copyright 2012-2023 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.boot.test.web.client;
+
+import java.util.function.Supplier;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import org.springframework.test.web.client.RequestExpectationManager;
+import org.springframework.test.web.client.SimpleRequestExpectationManager;
+import org.springframework.test.web.client.UnorderedRequestExpectationManager;
+import org.springframework.web.client.RestClient;
+import org.springframework.web.client.RestClient.Builder;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatIllegalArgumentException;
+import static org.assertj.core.api.Assertions.assertThatIllegalStateException;
+import static org.springframework.test.web.client.match.MockRestRequestMatchers.requestTo;
+import static org.springframework.test.web.client.response.MockRestResponseCreators.withSuccess;
+
+/**
+ * Tests for {@link MockServerRestClientCustomizer}.
+ *
+ * @author Scott Frederick
+ */
+class MockServerRestClientCustomizerTests {
+
+	private MockServerRestClientCustomizer customizer;
+
+	@BeforeEach
+	void setup() {
+		this.customizer = new MockServerRestClientCustomizer();
+	}
+
+	@Test
+	void createShouldUseSimpleRequestExpectationManager() {
+		MockServerRestClientCustomizer customizer = new MockServerRestClientCustomizer();
+		customizer.customize(RestClient.builder());
+		assertThat(customizer.getServer()).extracting("expectationManager")
+			.isInstanceOf(SimpleRequestExpectationManager.class);
+	}
+
+	@Test
+	void createWhenExpectationManagerClassIsNullShouldThrowException() {
+		Class<? extends RequestExpectationManager> expectationManager = null;
+		assertThatIllegalArgumentException().isThrownBy(() -> new MockServerRestClientCustomizer(expectationManager))
+			.withMessageContaining("ExpectationManager must not be null");
+	}
+
+	@Test
+	void createWhenExpectationManagerSupplierIsNullShouldThrowException() {
+		Supplier<? extends RequestExpectationManager> expectationManagerSupplier = null;
+		assertThatIllegalArgumentException()
+			.isThrownBy(() -> new MockServerRestClientCustomizer(expectationManagerSupplier))
+			.withMessageContaining("ExpectationManagerSupplier must not be null");
+	}
+
+	@Test
+	void createShouldUseExpectationManagerClass() {
+		MockServerRestClientCustomizer customizer = new MockServerRestClientCustomizer(
+				UnorderedRequestExpectationManager.class);
+		customizer.customize(RestClient.builder());
+		assertThat(customizer.getServer()).extracting("expectationManager")
+			.isInstanceOf(UnorderedRequestExpectationManager.class);
+	}
+
+	@Test
+	void createShouldUseSupplier() {
+		MockServerRestClientCustomizer customizer = new MockServerRestClientCustomizer(
+				UnorderedRequestExpectationManager::new);
+		customizer.customize(RestClient.builder());
+		assertThat(customizer.getServer()).extracting("expectationManager")
+			.isInstanceOf(UnorderedRequestExpectationManager.class);
+	}
+
+	@Test
+	void customizeShouldBindServer() {
+		Builder builder = RestClient.builder();
+		this.customizer.customize(builder);
+		this.customizer.getServer().expect(requestTo("/test")).andRespond(withSuccess());
+		builder.build().get().uri("/test").retrieve().toEntity(String.class);
+		this.customizer.getServer().verify();
+	}
+
+	@Test
+	void getServerWhenNoServersAreBoundShouldThrowException() {
+		assertThatIllegalStateException().isThrownBy(this.customizer::getServer)
+			.withMessageContaining("Unable to return a single MockRestServiceServer since "
+					+ "MockServerRestClientCustomizer has not been bound to a RestClient");
+	}
+
+	@Test
+	void getServerWhenMultipleServersAreBoundShouldThrowException() {
+		this.customizer.customize(RestClient.builder());
+		this.customizer.customize(RestClient.builder());
+		assertThatIllegalStateException().isThrownBy(this.customizer::getServer)
+			.withMessageContaining("Unable to return a single MockRestServiceServer since "
+					+ "MockServerRestClientCustomizer has been bound to more than one RestClient");
+	}
+
+	@Test
+	void getServerWhenSingleServerIsBoundShouldReturnServer() {
+		Builder builder = RestClient.builder();
+		this.customizer.customize(builder);
+		assertThat(this.customizer.getServer()).isEqualTo(this.customizer.getServer(builder));
+	}
+
+	@Test
+	void getServerWhenRestClientBuilderIsFoundShouldReturnServer() {
+		Builder builder1 = RestClient.builder();
+		Builder builder2 = RestClient.builder();
+		this.customizer.customize(builder1);
+		this.customizer.customize(builder2);
+		assertThat(this.customizer.getServer(builder1)).isNotNull();
+		assertThat(this.customizer.getServer(builder2)).isNotNull().isNotSameAs(this.customizer.getServer(builder1));
+	}
+
+	@Test
+	void getServerWhenRestClientBuilderIsNotFoundShouldReturnNull() {
+		Builder builder1 = RestClient.builder();
+		Builder builder2 = RestClient.builder();
+		this.customizer.customize(builder1);
+		assertThat(this.customizer.getServer(builder1)).isNotNull();
+		assertThat(this.customizer.getServer(builder2)).isNull();
+	}
+
+	@Test
+	void getServersShouldReturnServers() {
+		Builder builder1 = RestClient.builder();
+		Builder builder2 = RestClient.builder();
+		this.customizer.customize(builder1);
+		this.customizer.customize(builder2);
+		assertThat(this.customizer.getServers()).containsOnlyKeys(builder1, builder2);
+	}
+
+	@Test
+	void getExpectationManagersShouldReturnExpectationManagers() {
+		Builder builder1 = RestClient.builder();
+		Builder builder2 = RestClient.builder();
+		this.customizer.customize(builder1);
+		this.customizer.customize(builder2);
+		RequestExpectationManager manager1 = this.customizer.getExpectationManagers().get(builder1);
+		RequestExpectationManager manager2 = this.customizer.getExpectationManagers().get(builder2);
+		assertThat(this.customizer.getServer(builder1)).extracting("expectationManager").isEqualTo(manager1);
+		assertThat(this.customizer.getServer(builder2)).extracting("expectationManager").isEqualTo(manager2);
+	}
+
+}