Will Drupal & Drupal Commerce run under php-cgi?
Core in particular, but also Commerce, is extensively covered by automated tests. 

Many of those are also run in a style that simulates a users journey, not only unit tests. So if you run those, you will have exercised essentially all relevant code.

There are some things that are not covered though, such as CSS and JS, although I strongly doubt those are affected by how you run the php interpreter.

Setup a Drupal instance, enable the testing module, and execute all the tests. Go read a book (as that will take a long time), and hope that you come back to all green. :)