RStudio has several different varieties of unit tests, corresponding to the different kinds of code in the product; each of them are authored and run differently.

Unit tests are dev-authored and checked into the product repo. They are run by developers on their dev machines, and as part of the official builds.

Failed unit tests do not fail the build; they mark it as "(unstable)".

For integration testing (testing entire scenarios via Selenium) see the IDE Automation README.

Unit tests for the C++ and R code in the core libraries and session executables are described in CPP Unit Tests.

Unit tests for the GWT UI are described in GWT Unit Tests.