Do you use unit testing in wordpress development?

Yes, by maximizing the code that doesn't depend on the Wordpress framework or libraries. This makes it much easier to run tests on plain PHP code that doesn't even load Wordpress.

I do use unit testing for our WordPress plugin: https://github.com/LaunchKey/launchkey-wordpress. It currently uses a facade for interacting with all of the globals in WordPress to make it testable with https://github.com/mlively/Phake for object mocking. After speaking with at the most recent ZendCon, I am investigating switching to https://github.com/10up/wp_mock with https://github.com/padraic/mockery for object mocking. It's probably not the best example of unit testing WordPress you will find as this is my first time unit testing WordPress. As time goes by, the readability and quality of the tests will improve. Unit testing has its own merits especially with our project being open source. But, if I were delivering code to a client or not, I would still unit test code that I was not going to throw away. All code requires enhancements, bug fixes, and eventually refactoring. In order to perform those actions with confidence, unit tests are required. Another thing I plan to add to the tests is real world browser testing of the deployed plugin. I just haven't found a good methodology that will work within our security concerns.