http://weblogs.asp.net/adilakhter/archive/2008/05/04/more-on-unit-testing-testcontext.aspx
What is TestContext?
TestContext is a abstract class
of Microsoft.VisualStudio.TestTools.UnitTesting namespace that provides
various information about the current test run. Purposes that has been
served by TestContext Class -
1. To store information and provide information
to the unit tests during Unit Test Run.
2. Provide a mechanism to measure performance of
your code being tested by the Unit Test.
3. In Testing the web service it stores the additional information, like
server's URL.
4. In Asp.Net unit tests, it get holds of the Page object.
5. For Data Driven Unit Tests , it provides access to the data rows.