increasing coverage by adding another test

Signed-off-by: fahadshamiinsta <[email protected]>

plugins/repository-gcs/src/test/java/org/opensearch/repositories/gcs/GoogleCloudStorageServiceTests.java

@@ -245,6 +245,19 @@ public void applicationDefaultCredentialThrowsErrorWhenNotAvailable() throws Exc
         MatcherAssert.assertThat(exception.getMessage(), containsString("The Application Default Credentials are not available"));
     }
 
+    /**
+     * The application default credential throws exception when it is
+     * used without GoogleCloudStorageService
+     * @throws Exception
+     */
+    public void googleApplicationDefaultCredentialsThrowsExceptionWithoutGoogleCloudStorageService() throws Exception {
+        GoogleApplicationDefaultCredentials googleApplicationDefaultCredentials = new GoogleApplicationDefaultCredentials();
+        GoogleCredentials credentials = googleApplicationDefaultCredentials.get();
+        assertNull(credentials);
+        Exception exception = assertThrows(IOException.class, GoogleCredentials::getApplicationDefault);
+        MatcherAssert.assertThat(exception.getMessage(), containsString("The Application Default Credentials are not available"));
+    }
+
     /**
      * This is a helper method to provide GCS Client settings without credentials
      * @return