When a user with read-only credentials on a bucket connects and attempts to write a blob, it silently exits as if it succeeded even though nothing was written.

This service account has only read permissions on the bucket referenced (project and bucket name have been changed for this example).

credentials = ServiceAccountCredentials.from_json_keyfile_dict(credentials_dict)
client = storage.Client(credentials=credentials, project='testproject')
bucket = client.get_bucket('testbucket')
blob = bucket.blob('testblob')
blob.upload_from_string('this is a test blob\n')

Nothing gets uploaded, but the final function call exits with no indication of failure.