It would have been quite simple to mandate testing before boarding. It took a while, but in the EU it is now a general rule for many countries for air passengers to: take a test up to 72 hours before travel; or in some cases do the test at the airport of destination.
So simple one wonders why it took so long...
it will surely be a bit more secure, but you may caught it last week and still not be detected.
It is certainly not 100% waterproof- that is a problem with this virus.
The same on the returnflight. if you are negative then ; you probably did not cache it before you went away.
If you are positive- damage is done in the visiting country, but you know you can go into quarantaine for not exposing more people to the virus.
I understand every week a test would be best for everyone; but not very practical.