The following list of links and resources should be useful to complete your testing needs:

Utilise the capabilities of Visual Studios testing features:

First of all learn what team system has to offer: Loads of videos at www.asp.net : Getting Started with Team System

http://www.asp.net/learn/vsts-videos/

Testing SharePoint specialities

Testing SharePoint Alerts in a Test Environment

Free Utility for Testing SharePoint/MOSS 2007 Email Sending in a Development Environment.

http://blogs.officezealot.com/legault/archive/2006/02/02/9143.aspx

Testing SharePoint Search

This article nicely demonstrates how to use visual studios web tests to test SharePoint search:

http://www.helloitsliam.com/archive/2008/04/14/moss2007-–-visual-studio-2008-testing-search.aspx

Testing document upload

Apart from giving a good intro on how to use visual studio tests this article shows what is needed to upload documents in web tests, which really is not trivial.

http://www.helloitsliam.com/archive/2008/06/23/moss2007-testing-with-vs-2008-response-to-comments.aspx

SharePoint load testing & test data creation

http://blogs.msdn.com/edglas/archive/2007/02/17/sharepoint-load-tests.aspx

http://blogs.msdn.com/edglas/archive/2007/02/17/performance-testing-guidance.aspx

Unit Testing

Unit testing SharePoint code quickly becomes a challenge when your code uses the SharePoint context object. This usually involves some kind of mockup code. The following article describes the necessary steps to achieve this. (Actually the article is written for SharePoint 2003/WSS 2.0, but the pattern remains the same.)

http://blog.chapmanconsulting.ca/2006/02/15/Creating+An+NUnit+Base+Test+Class+For+SharePoint+Applications+Part+2.aspx

Layout / Web Testing

IE Tester

IETester is a free WebBrowser that allows you to have the rendering and javascript engines of IE8 beta 2, IE7 IE 6 and IE5.5 on Vista and XP, as well as the installed IE in the same process:

http://www.my-debugbar.com/wiki/IETester/HomePage

Browsershots

“Browsershots makes screenshots of your web design in different browsers. It is a free open-source online service created by Johann C. Rocholl. When you submit your web address, it will be added to the job queue. A number of distributed computers will open your website in their browser. Then they will make screenshots and upload them to the central server here.”
If you don’t like publishing your confidential designs to the internet, the you can either rent your own CPU time or set up your own instance.

http://v03.browsershots.org/

Alternative web testing method

If you can’t use visual studios testing features for some reason then have a look at WSSTester:

http://www.sharethispoint.com/archive/2008/01/22/Automated-Testing-in-SharePoint-with-WSSTester.aspx