Damian Conway gives some excellent Debugging advice in Ten Essential Development Practices namely:

Add New Test Cases Before You Start Debugging

The first step in any debugging process is to isolate the incorrect behaviour of the system, by producing the shortest demonstration of it that you reasonably can. Once you have distilled a short working example of the bug, convert it to a series of tests.

Don't try to fix the problem straight away, though. Instead, immediately add those tests to your test suite. The point is: if the original test suite didn't report this bug, then that test suite was broken. It simply didn't do its job (finding bugs) adequately. Fix the test suite first by adding tests that cause it to fail.

Once the test suite is detecting the problem correctly, then you'll be able to tell when you've correctly fixed the actual bug, because the tests will once again fall silent. The more thoroughly you test the bug, the more completely you will fix it.

External Debugger References

• Ten Essential Development Practices by Damian Conway
• Programming tool (wikipedia)
• I do not use a debugger (Daniel Lemire blog)
• Debuggers are a wasteful Timesink (Robert C Martin)
• The Tao of Debugging (John Graham-Cumming)
• The Best Programming Advice I Ever Got (Rob Pike)
• thornydev (Thoughts on Debuggers blog)
• Are You Still Debugging? (blog)

Perl Monks Debugger Nodes

• Are debuggers good?
• Using the Perl Debugger (-d)
• I like Python's interactive shell a lot better than Perl's debugger. What are my alternatives?
• In the art of Perl Debugger Mastery, I seek enlightenment
• Rambling about debuggers
• Driving maniacally with the debugger