| PASS TransformStream flush is called immediately when the writable is closed, if no writes are queued | |
| PASS TransformStream flush is called after all queued writes finish, once the writable is closed | |
| PASS TransformStream flush gets a chance to enqueue more into the readable | |
| PASS TransformStream flush gets a chance to enqueue more into the readable, and can then async close | |
| PASS error() during flush should cause writer.close() to reject | |