Customs first
Switzerland is a third country: the vehicle must be cleared through customs, and you receive the 846 A certificate required for registration. See before and after the RTI.
The COC is often enough
If your vehicle is a model sold in the European Union, its manufacturer can issue a European certificate of conformity. You then apply for registration without going through the DREAL. Order it on homologations.eu.
When the RTI is required
If the manufacturer cannot supply a COC, for example for a version specific to the Swiss market or a vehicle imported into Switzerland from another continent, the vehicle comes under the RTI.
The roadworthiness test
The ANTS accepts a roadworthiness test carried out in France or in a European Union country. So plan for a French test for a vehicle over 4 years old.
You are moving from Switzerland to France
Transferring your main residence gives entitlement to relief from duties and taxes, under conditions: having lived at least 12 months outside the European Union, and a non-commercial vehicle in your possession for more than 6 months. Customs then gives you the 846 A certificate.