Connect 230 or 115 VAC. Observe the LED's H1 and H2 which should be lit. Measure the output voltage without any load. It should be stable within the last digit on your DVM. If you want to trim the voltage you could either do it changing the reference voltage or if you have a fixed reference you can use R9 and R11.

Connect a load for getting 100 mA output current. 150 ohms for 15 volts. The voltage should still be stable and change very little compared to the voltage when without any load.

Measure the voltage between the raw voltage and the output. Should be at least 5 volts if the LM317 is used and 2-3 volts if not. Suitable test point is D1, cathode, just above the "+" connection of the rectifier bridge Br1.