Validate our own tests work with JUnit5 and the vintage engine

Closes gh-14737

Co-authored-by: Stephane Nicoll <snicoll@pivotal.io>

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

@@ -16,8 +16,7 @@
 
 package sample.devtools;
 
-import org.junit.Test;
-import org.junit.runner.RunWith;
+import org.junit.jupiter.api.Test;
 
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.boot.test.context.SpringBootTest;
@@ -25,7 +24,6 @@ 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.context.junit4.SpringRunner;
 
 import static org.assertj.core.api.Assertions.assertThat;
 
@@ -35,15 +33,14 @@ import static org.assertj.core.api.Assertions.assertThat;
  * @author Andy Wilkinson
  * @author Phillip Webb
  */
-@RunWith(SpringRunner.class)
 @SpringBootTest(webEnvironment = WebEnvironment.RANDOM_PORT)
-public class SampleDevToolsApplicationIntegrationTests {
+class SampleDevToolsApplicationIntegrationTests {
 
 	@Autowired
 	private TestRestTemplate restTemplate;
 
 	@Test
-	public void testStaticResource() {
+	void testStaticResource() {
 		ResponseEntity<String> entity = this.restTemplate
 				.getForEntity("/css/application.css", String.class);
 		assertThat(entity.getStatusCode()).isEqualTo(HttpStatus.OK);
@@ -51,7 +48,7 @@ public class SampleDevToolsApplicationIntegrationTests {
 	}
 
 	@Test
-	public void testPublicResource() {
+	void testPublicResource() {
 		ResponseEntity<String> entity = this.restTemplate.getForEntity("/public.txt",
 				String.class);
 		assertThat(entity.getStatusCode()).isEqualTo(HttpStatus.OK);
@@ -59,7 +56,7 @@ public class SampleDevToolsApplicationIntegrationTests {
 	}
 
 	@Test
-	public void testClassResource() {
+	void testClassResource() {
 		ResponseEntity<String> entity = this.restTemplate
 				.getForEntity("/application.properties", String.class);
 		assertThat(entity.getStatusCode()).isEqualTo(HttpStatus.NOT_FOUND);