I did not test my cooling system, but went looking for any leaks are drips following initial engine runs.
For fuel, the Facet pump has a non-return valve. I did my initial runs with wings off, so had the fuel return line blanked off, and that part of the system held pressure on the steam gauge after the pump had been run then turned off. (Incidentally, on normal prestart you are looking for that pressure to fall away quite promptly once the Facet pump is off: this tells you that the fuel return orifice is clear and doing it's job.)
I would be getting some gravity feed from wing height down into the receiver tank. Mine developed seepage from one of the tank top connectors and that wasn't evident until it began to wet the sides of the tank. So I would be looking hard at that area.
For the oil system, there is an essential Rotax priming procedure to push oil round the system after engine installation. This involves light pressurisation of the oil tank while turning the prop many times, and would allow you also to check for leaks.