Just to clarify:
FAA CPL requires ground study and passing the knowledge (theory) exam, and passing the practical test (checkride), consisting of an 'oral' portion, typically several hours worth, and a flight test, maybe 1.3-1.5 hrs in the plane.
The ground training can be accomplished by formal "ground school", or one-on-one with an instructor, or self-study using online or video course, or book(s). Each method requires the mentioned instructor endorsement prior to actually taking the exam. Also required is a second instructor endorsement attesting to the candidate's readiness to take the final practical test, signed by the flight training instructor. The self-study programs usually include that endorsement upon completion of the course, but there really is no direct monitoring of the student's knowledge, other than maybe completing all sections of the course. Years ago, the FAA did publish the entire question bank, and there were study programs that simply consisted of reviewing every question in a rote memory fashion, enabling test-passage, but maybe not ensuring any real retained knowledge. Now, the FAA no longer publishes the questions, but there are still study methods that present sample tests that are made up of similar questions. So, conceivably, a student with a minimal rote-learning could pass the knowledge exam, but whose knowledge deficiency would be (easily) caught by either their flight instructor prior to endorsement for the practical test, or at the last, by the examiner during the 'oral' portion of the checkride.