input: Write a function to calculate the area of a circle given its radius. If the radius is negative or zero, return 0. Include a test case.
  
  def area_circle(radius):
   if radius <= 0:
   return 0
   return math.pi * (radius ** 2)
  
  assert area_circle(5) == math.pi * 25
  assert area_circle(-2) == 0
  assert area_circle(0) == 0
output: def area_circle(radius):
      if radius <= 0:
          return 0
      return math.pi * (radius ** 2)