Fix expected error message googleapis#824

* Fix the expected error message that is tested when checking for requester pays buckets.
* The error message recieved when querying for requester pays status changed to include an 'a' which caused strict matching to fail.
* This fixes and standardizes the error message to use the same string for both the code and the tests.

google-cloud-nio/src/main/java/com/google/cloud/storage/contrib/nio/CloudStorageFileSystemProvider.java

@@ -89,6 +89,7 @@
 @AutoService(FileSystemProvider.class)
 public final class CloudStorageFileSystemProvider extends FileSystemProvider {
 
+  public static final String BUCKET_IS_REQUESTER_PAYS_ERROR_MESSAGE = "Bucket is a requester pays bucket but no user project provided";
   private Storage storage;
   private final StorageOptions storageOptions;
   // if non-null, we pay via this project.
@@ -971,7 +972,7 @@ public boolean requesterPays(String bucketName) {
       Boolean isRP = storage.get(bucketName).requesterPays();
       return isRP != null && isRP.booleanValue();
     } catch (StorageException ex) {
-      if (ex.getCode() == 400 && ex.getMessage().contains("Bucket is requester pays")) {
+      if (ex.getCode() == 400 && ex.getMessage().contains(BUCKET_IS_REQUESTER_PAYS_ERROR_MESSAGE)) {
         return true;
       }
       throw ex;

google-cloud-nio/src/test/java/com/google/cloud/storage/contrib/nio/it/ITGcsNio.java

@@ -266,7 +266,7 @@ private void innerTestCantCopyWithoutUserProject(
       Assert.assertTrue(
           description,
           hex.getMessage()
-              .contains("Bucket is requester pays bucket but no user project provided"));
+              .contains(CloudStorageFileSystemProvider.BUCKET_IS_REQUESTER_PAYS_ERROR_MESSAGE));
     } catch (StorageException ex) {
       assertIsRequesterPaysException(description, ex);
     }
@@ -319,14 +319,14 @@ private void assertIsRequesterPaysException(String message, StorageException ex)
     Assert.assertEquals(message, ex.getCode(), 400);
     Assert.assertTrue(
         message,
-        ex.getMessage().contains("Bucket is requester pays bucket but no user project provided"));
+        ex.getMessage().contains(CloudStorageFileSystemProvider.BUCKET_IS_REQUESTER_PAYS_ERROR_MESSAGE));
   }
 
   private void assertIsRequesterPaysException(String message, IOException ioex) {
     Assert.assertTrue(message, ioex.getMessage().startsWith("400"));
     Assert.assertTrue(
         message,
-        ioex.getMessage().contains("Bucket is requester pays bucket but no user project provided"));
+        ioex.getMessage().contains(CloudStorageFileSystemProvider.BUCKET_IS_REQUESTER_PAYS_ERROR_MESSAGE));
   }
   // End of tests related to the "requester pays" feature