What is Unit Testing?

Developer written automated tests of individual units of code to catch issues that are typically difficult to find with manual or automated QA.

Unit Tests are developer-written automated tests of individual units of code to catch issues that are typically difficult to find with manual or automated QA. Unit Tests are made up of code that runs other code in order to confirm that it is acting as expected. For instance, if a given function being used by the application should return the sum of two numbers, a unit test would make sure that 2+2 actually does return 4, 3+3 returns 6, -1+1 returns 0, and a few other similar tests with very small numbers and very large numbers. The code written for unit tests is typically written in the same language as the application itself. Unit Tests arent smoke tests or a quick once-over that developers should do before sending a build to QA. It also isnt manual QA or automated QA.