What Is a Unit Test? Where Unit Testing Came From and How to Write Good Ones

Tue, 20 Oct 2026 22:30:00 +0000

You change one line in a pricing function and want to know whether anything broke. You could start the whole application, log in, fill a cart and look at the total, for every kind of cart you can think of. Or you could run a few hundred small programs that each call the pricing function with one input and check the answer, and know in under a second. Those small programs are unit tests, and the second way of working is one of the biggest changes in how software has been written in the last thirty years: from testing as a phase at the end of a project, done by someone else, to testing as something every programmer does every few minutes.

TDD on Artur Rios Lab

What Is a Unit Test? Where Unit Testing Came From and How to Write Good Ones