Fix test for GCSStore#getOffset on 404 errors

Author: Acconut

lib/stores/GCSDataStore.js

@@ -183,7 +183,7 @@ class GCSDataStore extends DataStore {
         return new Promise((resolve, reject) => {
             const file = this.bucket.file(file_id);
             file.getMetadata((error, metadata, apiResponse) => {
-                if (error && error.message === 'Not Found') {
+                if (error && error.code === 404) {
                     return reject(ERRORS.FILE_NOT_FOUND);
                 }
 

test/Test-GCSDataStore.js

@@ -196,6 +196,7 @@ describe('GCSDataStore', () => {
         });
 
         it('should resolve existing files with the metadata', () => {
+            // TODO: upload this file to the bucket first
             return server.datastore.getOffset(FILE_ALREADY_IN_BUCKET)
                     .should.be.fulfilledWith({
                         size: TEST_FILE_SIZE,