Pull Request related notifications not appearing in Slack

Summary

Although Pull Request notifications on slack are configured for multiple branches in a repository, sometimes the notifications are not sent to slack.

Diagnosis

1. Set up Slack notifications for two channels #prod and #test in a repository. 

   1. This repository needs to have 4 branches "master", "dev", "test" and "qa". 

2. Set up Slack Notifications under Repository Settings for #prod channel and #test channel

   1. For #prod channel, the configuration is set up "Repository-wide".

      

   2. For #test channel, the configuration is set up for the "test" branch. 

      

3. Create a Pull Request from "test" branch to "master" branch. 

   1. The #prod channel receives a notification, the #test channel does not. 

      

4. Create a Pull Request from "qa" branch to "test" branch.

   1. #prod channel and #test channel both receive slack notifications. 

      1. #prod channel: 

         

      2. #test channel: 

         

5. Create a Pull Request from "test" branch to "dev" branch.

   1. #prod channel has a notification, #test channel does not.

      

Cause

Slack Notifications for Pull Requests run based on target branch configuration. This is why a Pull Request created from "test" branch to "dev" branch does not give a notification on the #test slack channel, because there is no Slack notification for Pull Request creation configured for "dev" branch. This applies to all Pull Request slack parameters. 

Solution

Ensure that slack notifications are configured for destination branches to generate Pull Request related slack notifications.