As explained in the article

http://www.dotnetjunkies.com/Tutorial/9709CE8B-0986-46D2-AE3B-5989F23D3A0F.dcik

by Doug Steven on www.dotnetjunkies.com

Red/Green/Refactor is the Test Driven Development (TDD) mantra.

Red: Write a failing test

Green: Write the code to satisfy the test

Refactor: Improve the code without changing the functionality

In other words:

Make it fail.  Make it work.  Make it better.

Tests need to provide coverage, but must be realistic.  Pinpoint an overall operation the application will attempt to solve, define the parameters, and test the outputs generated by the code.