In a previous post, I talked about my experiences with Automated Build Studio.  My company is looking at automated testing tools to help augment manual Q/A testing.  We’ve looked at TestComplete and thought about developing unit tests.  But with a codebase pushing 2 million lines of code, where do you begin writing unit tests?  And when you have pressures to deliver products, when do you find time to write unit tests?  How do you develop automated test scripts for a graphical CAD-type application?

What automated testing techniques do you use?  Did you use them from the start?  If not, when did you start adding tests to your codebase?  What approach did you take?