Provide TestRestTemplate for @WebIntegrationTests

Add a ContextCustomizerFactory to provide TestRestTemplate as a bean for
tests annotated with WebIntegrationTests. Additionally provide support
for automatically expanding URLs of the form `/example` to
`http://localhost:${local.server.port}/example`.

Fixes gh-5227

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

@@ -0,0 +1,61 @@
+/*
+ * Copyright 2012-2016 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
+ *
+ *      http://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 org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.ExpectedException;
+
+import org.springframework.mock.env.MockEnvironment;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link LocalHostUriTemplateHandler}.
+ *
+ * @author Phillip Webb
+ */
+public class LocalHostUriTemplateHandlerTests {
+
+	@Rule
+	public ExpectedException thrown = ExpectedException.none();
+
+	@Test
+	public void createWhenEnvironmentIsNullShouldThrowException() {
+		this.thrown.expect(IllegalArgumentException.class);
+		this.thrown.expectMessage("Environment must not be null");
+		new LocalHostUriTemplateHandler(null);
+	}
+
+	@Test
+	public void getBaseUrlShouldUseLocalServerPort() throws Exception {
+		MockEnvironment environment = new MockEnvironment();
+		environment.setProperty("local.server.port", "1234");
+		LocalHostUriTemplateHandler handler = new LocalHostUriTemplateHandler(
+				environment);
+		assertThat(handler.getBaseUrl()).isEqualTo("http://localhost:1234");
+	}
+
+	@Test
+	public void getBaseUrlWhenLocalServerPortMissingShouldUsePort8080() throws Exception {
+		MockEnvironment environment = new MockEnvironment();
+		LocalHostUriTemplateHandler handler = new LocalHostUriTemplateHandler(
+				environment);
+		assertThat(handler.getBaseUrl()).isEqualTo("http://localhost:8080");
+	}
+
+}