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On an intra-Schengen, intra-EU arrival, I was met on arrival by customs agents (like in most smaller aerodromes in France, immigration checks are delegated to the customs agency); they checked IDs and for negative COVID19 tests.
They provided a preprinted certification form for the passengers and crew to sign to certify they are free of COVID19 symptoms, and that they will self-quarantine after arrival. That was a nice gesture; the decree establishing these obligations says these certifications have to be signed before departure. I pointed out that the self-quarantine part does not apply to arrivals from the EU, they accepted that with good grace and let me cross out that part in the certification.
They good-naturedly acknowledged that the requirement for negative COVID19 test and written certification is stricto sensu not legally applicable to arrivals by air that are not CAT (nor, for that matter, to crew), but that the instructions from their hierarchy was to (call the Gendarmerie for them to) issue a fine to arrivals that don't have them (including crew, if the crew intends to enter France), and that they would have done that, irrespective of the certainty that the fine would not be upheld if contested in court. After the fine:
* arrivals from the EU are free to leave (e.g. back to origin) or enter quarantine in France (one would be allowed to quarantine at a place of one's own choosing)
* arrivals from outside the EU are refused entry
