Software Testing - Free License for Open Source Developers

..Net Unit Testing:

The advantages of unit testing are well known, giving development
teams a safety net to facilitate change, ease integration and supply
live documentation.Unit testing of small logical code is quite easy
and can show value quickly.
But in real life, our code will use other classes and components. If
this happens, things can get quite fragile and the tests will quickly
become system tests.
Typemock Isolator enables developers to unit test all their code by
magically disconnecting and isolating external components.
Typemock Isolator uses aspect-oriented technology to redirect calls
from the real code. This enables developers to define the behavior of
the external component required for a tested scenario. For example,
you can simulate that the disk is full when writing to a database by
instructing Typemock Isolator to throw an OutOfDiskSpaceException when
writing to the database. This is a scenario that will be nearly
impossible to test without Typemock Isolator. The developer defines
the behavior in the actual unit test and Typemock Isolator
automatically isolates all required components.

http://www.typemock.com/learn_about_..._isolator.html - Free
License for Open Source Developers.