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-flyway/src/test/java/sample/flyway/SampleFlywayApplicationTests.java

@@ -16,25 +16,22 @@
 
 package sample.flyway;
 
-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;
 import org.springframework.jdbc.core.JdbcTemplate;
-import org.springframework.test.context.junit4.SpringRunner;
 
 import static org.assertj.core.api.Assertions.assertThat;
 
-@RunWith(SpringRunner.class)
 @SpringBootTest
-public class SampleFlywayApplicationTests {
+class SampleFlywayApplicationTests {
 
 	@Autowired
 	private JdbcTemplate template;
 
 	@Test
-	public void testDefaultSettings() {
+	void testDefaultSettings() {
 		assertThat(this.template.queryForObject("SELECT COUNT(*) from PERSON",
 				Integer.class)).isEqualTo(1);
 	}