Testing according to the “extreme programming approach”

Extreme programming proposes another approach to white box testing.  I’ve found it interesting, so I’ve entered it here :

Most code in a system is unit tested, but not necessarily all paths through the code. Extreme programming mandates a “test everything that can possibly break” strategy, over the traditional “test every execution path” method. This leads developers to develop fewer tests than classical methods, but this isn’t really a problem, more a restatement of fact, as classical methods have rarely ever been followed methodically enough for all execution paths to have been thoroughly tested.[citation needed] Extreme programming simply recognizes that testing is rarely exhaustive (because it is often too expensive and time-consuming to be economically viable) and provides guidance on how to effectively focus limited resources.

Source :
https://en.wikipedia.org/wiki/Unit_testing#Unit_testing_limitations