Most people use Unit Test to run automatically during the build phase of the project. They provide built in regression testing, allow developers to analyze the code while writing the test, etc. One over looked analysis is seeing what sort of set up is required just to get the test to run. If your Unit Test requires defining and initializing of a large number of external systems (especially those that on the surface don’t seem like they should have anything to do with the system you are testing), you have a design issue. Your application is not Orthogonal, and perhaps a redesign is in order. This is particularly true with static elements of a system (this include Singeltons). As a full suite of tests may rely on the state of an external system not changing, which can’t be guaranteed with static globals.
So, next time you are writing a unit test, take a hard look at your set-up phase and make sure it doesn’t seem overly complicated. If it is, your system is not orthogonal and you are going to have problems if you don’t take care of them.
