Ask HN: What do you use to keep track of test cases for unit testing web apps?

Here's a slimmed-down example of a test case that I need to write down + perform:

======= Test: Response header is correct for custom 404

1) Enable debugging in Visual Studio

2) Set a breakpoint at Application_Error()

3) Enable the Firefox user agent switcher - switch to a new agent

4) Launch Fiddler

5) Browse to http://myurl/

6) If logged in, log out

7) Browse to http://myurl/filethatdoesnotexist.aspx

Expected result: 404 custom error page + logging in IIS of the 404 + breakpoint hit + headers report 404

=======

* This isn't a legit test case - but it's the kind of thing that Selenium can't really do (that I know of). And sometimes I also want to do other things at various points during the test - things that require manually stopping/pausing the test (maybe I want to repeat steps 3-6 n times, once for several other user agents for example).

How do you handle this sort of thing?