Added testing section to readme

Author: dimitribouniol

README.md

@@ -158,6 +158,18 @@ OPTIONS:
 
 TBD
 
+### Registering Subscribers
+
+TBD
+
+### Sending Messages
+
+TBD
+
+### Testing
+
+The `WebPushTesting` module can be used to obtain a mocked `WebPushManager` instance that allows you to capture all messages that are sent out, or throw your own errors to validate your code functions appropriately. Only import `WebPushTesting` in your testing targets.
+
 ## Contributing
 
 Contribution is welcome! Please take a look at the issues already available, or start a new discussion to propose a new feature. Although guarantees can't be made regarding feature requests, PRs that fit within the goals of the project and that have been discussed beforehand are more than welcome!