phpAsserUnit is a unit testing framework based on jsAsserUnit. It's a kind of wrapper of the assertion methods found in jsAsserUnit. So it provides the same functionalities, but in a PHP development environment. The first major difference is that assertion methods don't return a boolean value as a result of the assertion checking. This limitation could be removed in future versions. The second major difference is that phpAsserUnit doesn't provide the type testing methods found in jsAsserUnit, because similar functions are already part of the core PHP functions (is_string, is_numeric, etc.) Otherwise, the methods of the ASSERT_Tester singleton class actually are wrapping the methods of jsAsserUnit, hence the same behaviour, including the overloading mechanism. Relying on the JavaScript Assertion Unit Framework makes the design of phpAsserUnit very simple: there is only one class in the PHP package containing the ASSERT_Tester class, similar to the class with the same name in jsAsserUnit. This class is found in the assert.mod file (the mod extension signifies module).