Working voltage is the keyword you are looking for. There is a relation by the test voltage specifications of various safety standards. But the characterization of devices with isolation works basically the other way around. You are targeting a specific working voltage (e.g 1200 V, DC or AC, basic or reinforced insulation, possibly required to be partial discharge free). Then choose insulation thickness and creepage distances and select a test voltage according to applicable safety standards.
For basic insulation, you'll end up with at least 3000 V (4250 Peak) test voltage.
Instead of guessing about a possible working voltage from isolation test specifications, you would ask the manufacturer for devices suited for 1200 V working voltage, possibly with additional conditions as mentioned above.