Write a function to find the top or bottom surface area of a cylinder.
def topbottom_surfacearea(r):
  toporbottomarea=3.1415*r*r
  return toporbottomarea
<s>[INST]<<SYS>>Given a task and its code, generate test cases for the code.<</SYS>>Write a function to find the top or bottom surface area of a cylinder.
def topbottom_surfacearea(r):
  toporbottomarea=3.1415*r*r
  return toporbottomarea[/INST]assert topbottom_surfacearea(10)==314.15000000000003
assert topbottom_surfacearea(5)==78.53750000000001
assert topbottom_surfacearea(4)==50.264</s>