The testing module

The test program pep-build --test builds: a main that lists the entry file’s [Test] functions or runs one of them.

A test build loads testing into every file, as --import testing would, and adds to the entry file a main (marked [TestMain], which replaces the file’s own) that registers each [Test] function with a TestRunner and calls run. Test files do not import it themselves: the checks they call, such as expect_equal, are in the prelude, and the fixture TempFolder (a scratch folder removed when released) is here.

pep-test (pepper test) drives the program: it lists the tests with --list and runs each in a child process of its own with --run NAME (see the testing chapter).

Source: runtime/testing/module.pep