Php/docs/internals2.structure.tests
From Get docs
Testing an extension
One of the accepted requirements of good programming is testing. PHP provides a test harness for unit regression tests, in the form of a script called run-tests.php.
Tests for a particular module are stored in the tests/
subdirectory of the module's folder, and have a .phpt
extension. For details of the PHPT format, see
» https://qa.php.net/.