FranH

Dummy payment gateway for developers. Simulates IPN. Always marks Order as paid.
Useful for testing and developing. Never use it on live sites!

WooFakePay

Dummy payment gateway for developers. Simulates IPN. Always marks Order as paid.

Lee Blue

Pound makes it really easy to write and run unit tests for WordPress plugins.

Pound :: Easy Unit Testing For WordPress

We need to start writing testable code in WordPress plugins! There are very few academic projects in this area, and Lee Blue has put forward a really cool plugin here. This plugin takes a unique approach in that it is extremely simple and limited in what it can do. It's a great start for programmers looking to get into testing their plugins. 

Awesome start!

Easily write unit tests for WordPress plugins

WooFakePay vs Pound :: Easy Unit Testing For WordPress