Write a function to find the area of a rectangle.
def rectangle_area(l,b):
  area=l*b
  return area
<s>[INST]<<SYS>>Given a task and its code, generate test cases for the code.<</SYS>>Write a function to find the area of a rectangle.
def rectangle_area(l,b):
  area=l*b
  return area[/INST]assert rectangle_area(10,20)==200
assert rectangle_area(10,5)==50
assert rectangle_area(4,2)==8</s>