Testing can currently be executed only against a running installation of PhPeace.
It cannot be run from a source repository copy, until a proper installation automated script is written (#156).
To execute the test suite, run phtest.sh from the command-line.
The test framework is based on PhpUnit.
Put your test classes in tests, inheriting from PHPUnit_TestCase. See phpeace.php as an example.
Then edit the test script, including your classes and adding them to the $classes array. All their methods will be executed.
