Add test for devtools + serving from `/public`

Add a simple test to show that basic serving of `/public` resources
works with devtoos.

See gh-7752

spring-boot-samples/spring-boot-sample-devtools/src/main/resources/public/public.txt

@@ -0,0 +1 @@
+public file

spring-boot-samples/spring-boot-sample-devtools/src/test/java/sample/devtools/SampleDevToolsApplicationIntegrationTests.java

@@ -16,11 +16,48 @@
 
 package sample.devtools;
 
+import org.junit.Test;
+import org.junit.runner.RunWith;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.boot.test.context.SpringBootTest.WebEnvironment;
+import org.springframework.boot.test.web.client.TestRestTemplate;
+import org.springframework.http.HttpStatus;
+import org.springframework.http.ResponseEntity;
+import org.springframework.test.annotation.DirtiesContext;
+import org.springframework.test.context.junit4.SpringRunner;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
 /**
  * Integration tests for {@link SampleDevToolsApplication}.
  *
  * @author Andy Wilkinson
+ * @author Phillip Webb
  */
+@RunWith(SpringRunner.class)
+@SpringBootTest(webEnvironment = WebEnvironment.RANDOM_PORT)
+@DirtiesContext
 public class SampleDevToolsApplicationIntegrationTests {
 
+	@Autowired
+	private TestRestTemplate restTemplate;
+
+	@Test
+	public void testStaticResource() throws Exception {
+		ResponseEntity<String> entity = this.restTemplate
+				.getForEntity("/css/application.css", String.class);
+		assertThat(entity.getStatusCode()).isEqualTo(HttpStatus.OK);
+		assertThat(entity.getBody()).contains("color: green;");
+	}
+
+	@Test
+	public void testPublicResource() throws Exception {
+		ResponseEntity<String> entity = this.restTemplate.getForEntity("/public.txt",
+				String.class);
+		assertThat(entity.getStatusCode()).isEqualTo(HttpStatus.OK);
+		assertThat(entity.getBody()).contains("public file");
+	}
+
 }