Good unit test properties

1. A basic unit test:

• does not depend on the environment; e.g. it will run on your computer and it will run on your colleague’s computer

• does not depend on other unit tests

• does not depend on external data

• does not have side effects

2. A good unit test:

• asserts the results of your code

• tests a single unit of work (mostly a method)

• Covers all the paths of the code you want to test

3. A better unit test:

• tests and asserts edge cases and different ranges of data

• runs fast (< 100ms)

• is well-factored

A unit test should have the following properties:

• It should be automated and repeatable.

• It should be easy to implement.

• It should be relevant tomorrow.

• Anyone should be able to run it at the push of a button.

• It should run quickly.

• It should be consistent in its results (it always returns the same result if you

  don’t change anything between runs).

• It should have full control of the unit under test.

• It should be fully isolated (runs independently of other tests).

• When it fails, it should be easy to detect what was expected and determine how

  to pinpoint the problem.