Migrating "GcsSampleApplicationIntegrationTests.java" to JUnit5 (#867)

* migrating the test

* adding google checkstyle

spring-cloud-gcp-samples/spring-cloud-gcp-storage-resource-sample/src/test/java/com/example/GcsSampleApplicationIntegrationTests.java

@@ -17,8 +17,6 @@
 package com.example;
 
 import static org.assertj.core.api.Assertions.assertThat;
-import static org.hamcrest.Matchers.is;
-import static org.junit.Assume.assumeThat;
 
 import com.google.api.gax.paging.Page;
 import com.google.cloud.storage.Blob;
@@ -28,29 +26,30 @@
 import java.nio.charset.StandardCharsets;
 import java.util.concurrent.TimeUnit;
 import org.awaitility.Awaitility;
-import org.junit.After;
-import org.junit.Before;
-import org.junit.BeforeClass;
-import org.junit.Test;
-import org.junit.runner.RunWith;
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.condition.EnabledIfSystemProperty;
+import org.junit.jupiter.api.extension.ExtendWith;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.beans.factory.annotation.Value;
 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.test.context.junit4.SpringRunner;
+import org.springframework.test.context.junit.jupiter.SpringExtension;
 
 /**
  * This verifies the sample application for using GCP Storage with Spring Resource abstractions.
  *
  * <p>To run the test, set the gcs-resource-test-bucket property in application.properties to the
  * name of your bucket and run: mvn test -Dit.storage
  */
-@RunWith(SpringRunner.class)
+@EnabledIfSystemProperty(named = "it.storage", matches = "true")
+@ExtendWith(SpringExtension.class)
 @SpringBootTest(
     webEnvironment = WebEnvironment.RANDOM_PORT,
     classes = {GcsApplication.class})
-public class GcsSampleApplicationIntegrationTests {
+class GcsSampleApplicationIntegrationTests {
 
   @Autowired private Storage storage;
 
@@ -59,26 +58,17 @@ public class GcsSampleApplicationIntegrationTests {
   @Value("${gcs-resource-test-bucket}")
   private String bucketName;
 
-  @BeforeClass
-  public static void checkToRun() {
-    assumeThat(
-        "Google Cloud Storage Resource integration tests are disabled. "
-            + "Please use '-Dit.storage=true' to enable them. ",
-        System.getProperty("it.storage"),
-        is("true"));
-  }
-
-  @Before
-  @After
-  public void cleanupCloudStorage() {
+  @BeforeEach
+  @AfterEach
+  void cleanupCloudStorage() {
     Page<Blob> blobs = this.storage.list(this.bucketName);
     for (Blob blob : blobs.iterateAll()) {
       blob.delete();
     }
   }
 
   @Test
-  public void testGcsResourceIsLoaded() {
+  void testGcsResourceIsLoaded() {
     BlobId blobId = BlobId.of(this.bucketName, "my-file.txt");
     BlobInfo blobInfo = BlobInfo.newBuilder(blobId).setContentType("text/plain").build();
     this.storage.create(blobInfo, "Good Morning!".getBytes(StandardCharsets.UTF_8));