Getting Started with Unit Testing

Question

Unit testing is, roughly speaking, testing bits of your code in isolation with test code. The immediate advantages that come to mind are:

• Running the tests becomes automate-able and repeatable
• You can test at a much more granular level than point-and-click testing via a GUI

Rytmis

My question is, what are the current "best practices" in terms of tools as well as when and where to use unit testing as part of your daily coding?

Lets try to be somewhat language agnostic and cover all the bases.

Answer 1

Ok here's some best practices from some one who doesn't unit test as much as he should...cough.

1. Make sure your tests test one thing and one thing only.
2. Write unit tests as you go. Preferably before you write the code you are testing against.
3. Do not unit test the GUI.
4. Separate your concerns.
5. Minimise the dependencies of your tests.
6. Mock behviour with mocks.

Answer 2

You might want to look at TDD on Three Index Cards and Three Index Cards to Easily Remember the Essence of Test-Driven Development:

Card #1. Uncle Bob’s Three Laws

• Write no production code except to pass a failing test.
• Write only enough of a test to demonstrate a failure.
• Write only enough production code to pass the test.

Card #2: FIRST Principles

• Fast: Mind-numbingly fast, as in hundreds or thousands per second.
• Isolated: The test isolates a fault clearly.
• Repeatable: I can run it repeatedly and it will pass or fail the same way each time.
• Self-verifying: The Test is unambiguously pass-fail.
• Timely: Produced in lockstep with tiny code changes.

Card #3: Core of TDD

• Red: test fails
• Green: test passes
• Refactor: clean code and tests