Unit Test: 409 server error

[beaucollins]

Unit test to simulate a client receiving a 409 error from the server for a change that originated from the same client.

The fix is intentionally left out which should be as simple as:

diff --git a/src/simperium/channel.js b/src/simperium/channel.js
index 4f59d15..15db61b 100644
--- a/src/simperium/channel.js
+++ b/src/simperium/channel.js
@@ -238,6 +238,7 @@ internal.handleChangeError = function( err, change, acknowledged ) {
 			}
 
 			break;
+		case 409:
 		case CODE_EMPTY_RESPONSE: // Change causes no change, just acknowledge it
 			internal.updateAcknowledged.call( this, acknowledged );
 			break;

[beaucollins]

Without this, any future channel.emit('acknowledge') causes a test to error because done is called more than once.

[beaucollins]

See: https://github.com/Simperium/simperium-protocol/blob/master/SYNCING.md#receiving-remote-changes

c:[{"clientid":"offending-client","id":"object-key","error":"401","ccids":["abcdef123456"]}]

[beaucollins]

Worth noting in the protocol docs it says:

409 : Duplicate change, client should stop sending this change and retrieve changes since its last syncd cv to process the changes list from the server. In normal case the remote changes list will contain the change that caused the duplicate error. If it doesn't, client will need to re-load this object. In either case, client will know that the server version of the object already incorporates the delta that this change contains.

[dmsnell]

I left this as a separate case since it carries a different semantic meaning than an empty change

[dmsnell]

Let's and continue tracking the errors. This doesn't solve the problem I found in Automattic/simplenote-electron#1579 but it does seem to be a hidden bug.