This is intended to be a brief overview of some of the things you need to do think about when doing QA/testing a website or web application. It is aimed more at the front-end than the back-end, and is not comprehensive (but should still serve as an excellent guide).
Turn off Javascript and browse the site. Can you get everywhere? Does anything look really weird? Should it be fixed?
Turn off
CSS and do the same thing (or browse the site in a text based browser). Folks with screen readers will be browsing your site this way: does it at least make sense?
Clear & disable cookies. Does your site still work? If you need cookies to use your site, are the 'cookies disabled' error messages at least helpful?
Test that characters are properly encoded before being stored in the DB, and properly decoded when coming out of the DB.
Test for
SQL injection vulnerabilities.
Turn off your database. Does your app error gracefully if the DB is down?
Test that you (or someone) gets an email for every address on the site. Note that is not just good enough to send a message and make sure it doesn't bounce; you need to send a message that says 'please reply' and then followup to make sure you actually get a reply.
Call every phone number on the site and make sure it is correct.
This is optional, but you may want to make sure your pages validate against the
W3C Validator.
Run
PHP with errors set on
E_ALL. That will make sure you don't have any
E_NOTICE level warnings. Optionally, run it on
E_STRICT
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