Make TestRestTemplate not extend RestTemplate

Update TestRestTemplate so that it no longer directly extends
RestTemplate. Prior to this commit it was possible that TestRestTemplate
could interfere with user defined RestTemplate beans.

TestRestTemplate offers the same methods as RestTemplate so should be
a drop-in replacement. If access is needed to the actual underlying
template the `getRestTemplate()` method should be used.

Fixes gh-5915

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

@@ -16,15 +16,24 @@
 
 package org.springframework.boot.test.web.client;
 
+import java.lang.reflect.Method;
+import java.net.URI;
+
 import org.apache.http.client.config.RequestConfig;
 import org.junit.Test;
 
 import org.springframework.boot.test.web.client.TestRestTemplate.CustomHttpComponentsClientHttpRequestFactory;
 import org.springframework.boot.test.web.client.TestRestTemplate.HttpClientOption;
+import org.springframework.http.HttpMethod;
 import org.springframework.http.client.HttpComponentsClientHttpRequestFactory;
 import org.springframework.http.client.InterceptingClientHttpRequestFactory;
+import org.springframework.util.ReflectionUtils;
+import org.springframework.util.ReflectionUtils.MethodCallback;
+import org.springframework.web.client.RestOperations;
+import org.springframework.web.client.RestTemplate;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.Mockito.mock;
 
 /**
  * Tests for {@link TestRestTemplate}.
@@ -37,14 +46,15 @@ public class TestRestTemplateTests {
 	@Test
 	public void simple() {
 		// The Apache client is on the classpath so we get the fully-fledged factory
-		assertThat(new TestRestTemplate().getRequestFactory())
+		assertThat(new TestRestTemplate().getRestTemplate().getRequestFactory())
 				.isInstanceOf(HttpComponentsClientHttpRequestFactory.class);
 	}
 
 	@Test
 	public void authenticated() {
-		assertThat(new TestRestTemplate("user", "password").getRequestFactory())
-				.isInstanceOf(InterceptingClientHttpRequestFactory.class);
+		assertThat(new TestRestTemplate("user", "password").getRestTemplate()
+				.getRequestFactory())
+						.isInstanceOf(InterceptingClientHttpRequestFactory.class);
 	}
 
 	@Test
@@ -52,9 +62,59 @@ public class TestRestTemplateTests {
 		TestRestTemplate template = new TestRestTemplate(
 				HttpClientOption.ENABLE_REDIRECTS);
 		CustomHttpComponentsClientHttpRequestFactory factory = (CustomHttpComponentsClientHttpRequestFactory) template
-				.getRequestFactory();
+				.getRestTemplate().getRequestFactory();
 		RequestConfig config = factory.getRequestConfig();
 		assertThat(config.isRedirectsEnabled()).isTrue();
 	}
 
+	@Test
+	public void restOperationsAreAvailable() throws Exception {
+		RestTemplate delegate = mock(RestTemplate.class);
+		final TestRestTemplate restTemplate = new TestRestTemplate(delegate);
+		ReflectionUtils.doWithMethods(RestOperations.class, new MethodCallback() {
+
+			@Override
+			public void doWith(Method method)
+					throws IllegalArgumentException, IllegalAccessException {
+				Method equivalent = ReflectionUtils.findMethod(TestRestTemplate.class,
+						method.getName(), method.getParameterTypes());
+				try {
+					equivalent.invoke(restTemplate,
+							mockArguments(method.getParameterTypes()));
+				}
+				catch (Exception ex) {
+					throw new IllegalStateException(ex);
+				}
+			}
+
+			private Object[] mockArguments(Class<?>[] parameterTypes) throws Exception {
+				Object[] arguments = new Object[parameterTypes.length];
+				for (int i = 0; i < parameterTypes.length; i++) {
+					arguments[i] = mockArgument(parameterTypes[i]);
+				}
+				return arguments;
+			}
+
+			private Object mockArgument(Class<?> type) throws Exception {
+				if (String.class.equals(type)) {
+					return "String";
+				}
+				if (Object[].class.equals(type)) {
+					return new Object[0];
+				}
+				if (URI.class.equals(type)) {
+					return new URI("http://localhost");
+				}
+				if (HttpMethod.class.equals(type)) {
+					return HttpMethod.GET;
+				}
+				if (Class.class.equals(type)) {
+					return Object.class;
+				}
+				return mock(type);
+			}
+
+		});
+
+	}
 }