Magento 1 Testing Frameworks

We are using the EcomDev_PHPUnit extension which allows you to test almost everything in Magento without modifying any core files.

I recommend the dev branch which is currently more stable than the master.

We also have experience with Mage-Test, but can not recommend it, because it overwrites some core files in the community codePool.

If you want something very simple and quick to setup, take a look at Testify

I used it in one of my projects to quickly test Model and Helper methods. For an example on how to run it with Magento, check: https://github.com/erfanimani/Ezimport/blob/master/tests/test.php

You could also look at extending the Magento Test Automation Framework which has over 1000 functional tests and which is used to check Magento Community Edition's nightly builds http://www.magentocommerce.com/blog/comments/automate-your-testing-with-the-magento-test-automation-framework/