For the modules you want Test::More and friends. A good introduction is Test::Tutorial.

For testing the web application itself WWW::Mechanize is very useful, and people have said good things about HTTP::WebTest. You may also find Test::HTML::Content and Test::HTML::Lint of interest.

On perlmonks try:

• The Joy of Test
• Automated software testing: emulation of interfaces using Test::MockObject
• Unit Testing Generated HTML
• What goes in a test suite?
• Further adventures with testing
• Micro Mocking: using local to help test subs

Hope this helps.