Four To The Floor - Test frustration

There are two outcomes for my test, either "ErrorTooLongForProcess" or I fail this test: "assert(is_covered([300,150],[[40,60,240],[240,140,100],[295,10,50]])) == False"

My Code:

def is_covered(room, sensors):
    step = 0.2
    for i in numpy.arange(0, room[0]+step, step):
        for j in numpy.arange(0, room[1]+step, step):
            if not check_sensor(sensors, 0, i, j):
                return False
    return True


def check_sensor(sensor, current, i, j):
    if current == len(sensor):
        return False
    if not (i - sensor[current][0]) ** 2 + (j - sensor[current][1]) ** 2 <= sensor[current][2] ** 2:
        return check_sensor(sensor, current+1, i, j)
    else:
        return True

This one is "ErrorTooLongForProcess", if I change step to 0.3 it fails the test. Ok I could test anything in between, but I don't think, thats the plan. Any help?