First place I'd start would be to write a test for every bug in your bug database, closed or not. For one thing, you guarantee that the bug that was fixed 4 years ago is still fixed. The other reason is that you start to write tests for every subsytem that's being used. (If it isn't being used, then who cares if it has bugs or not?) This gives you ideas for tests that aren't specifically for bugs in your bug tracker. Maybe the bug is a specific instance of a general case and the fix didn't fix the general case.
in reply to What is the best way to add tests to existing code?
Other than that, you pretty much have the list down.
We are the carpenters and bricklayers of the Information Age.
Then there are Damian modules.... *sigh* ... that's not about being less-lazy -- that's about being on some really good drugs -- you know, there is no spoon. - flyingmoose
I shouldn't have to say this, but any code, unless otherwise stated, is untested