For test flights, I would not put the flaps down at take-off. Just be sure you have plenty of airspeed and lift the aircraft off gently.

One thing I see almost every time I go to the field is people who won't abort a bad take-off run. They zig-zag all over the field and instead of cutting the throttle and taxiing back for another attempt, they take off with too little airspeed, cross-wind, down-wind, you name it.

Point being that you should be ready to abort if you don't like the run. Too much work in a scale ship to try to force it in the air.

If you feel compelled to use flap on the test flight, I would say no more than 10 - 15 degrees.