Unit testing and using the mocking pattern are new to my team and I.  After talking with Ron Shoshani at TypeMock they decided put a video up for beginners.

This video shows you how to break constructor dependency when writing unit tests.  Constructor dependency is when you one object depends on another during the creation or construction.  When another object is used in the constructor it binds the classes together in a way that makes testing discrete concerns more difficult.

To solve this problem without TypeMock developers would use the Mock Object Pattern.  Usually through the use of interfaces a class is created for the use in the test that mocks or mimics what the real functionality would be.  Usually this is a simple implementation that does not actually perform the true work that would be needed to implement the interface.  The implementation would be just enough to complete the unit tests that use it. This new implementation would then be used in the unit test of the class you wanted to test.

With TypeMock you will be able to mock objects that do not have interfaces, and even more powerful you don't even have to create the mock object implementation.  This makes testing objects that have dependant objects much easier to test.

If you have not checked out TypeMock you should do so.