Unit Testing

In computer programming, unit testing is a software testing method by which individual units of source code, sets of one or more computer program modules together with associated control data, usage procedures, and operating procedures, are tested to determine whether they are fit for use.

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 get a safety net for your existing code
• You can easily refactor your code and cover the different unit functinality
• You can test at a much more granular level than point-and-click testing via a GUI

Note that if your test code writes to a file, opens a database connection or does something over the network, it's more appropriately categorized as an integration test. Integration tests are a good thing, but should not be confused with unit tests. Unit test code should be short, sweet and quick to execute.

Another way to look at unit testing is that you write the tests first. This is known as Test-Driven Development (TDD for short). TDD brings additional advantages:

• You don't write speculative "I might need this in the future" code -- just enough to make the tests pass
• The code you've written is always covered by tests
• By writing the test first, you're forced into thinking about how you want to call the code, which usually improves the design of the code in the long run.