A quick guide to customizing work items in Team Foundation Server:

1: Install Team Foundation Server Power Tools.

2:  In Visual Studio, connect to your TFS collection and open the Work Item Template definition on the server:

3: Select the work item template you want to edit:

4: Today, I added a “Pass/Fail” field to test case.  Click “New” to add a new field.

5: You can specify a number of field types such as text, number, dropdown, etc.  For a dropdown, specify a list of allowed values in the “Rules” tab

 

6: After you add a new field, you need to add it to the layout:

7:  You can also define rules for workflow transitions that depend on your new field: