The electronic test (E-Test) for circuit boards is performed after manufacture. Your circuit boards are checked with a flying probe, or for larger series using an adapter E-Test. 
The layout is analysed according to the net list (from the Gerber data) for short circuits and interruptions.
This is extremely important, because only the E-Test can recognize incorrect and missing connections, meaning that without the E-Test, the usability of your circuit board is just a random chance!
Circuit boards that are identified as defective are eliminated; defective circuit boards in panels are specially marked.
Your advantage with Multi PCB is that the E-Test is always included for 2 or more layers!
It is a common mistake to believe that once a circuit board has been manufactured error-free, it no longer needs to be subjected to an E-Test. Since each production of a circuit board charge is a separate process, it is necessary to test every time!
