Write a function to find minimum of three numbers.
def min_of_three(a,b,c): 
      if (a <= b) and (a <= c): 
        smallest = a 
      elif (b <= a) and (b <= c): 
        smallest = b 
      else: 
        smallest = c 
      return smallest 
<s>[INST]<<SYS>>Given a task and its code, generate test cases for the code.<</SYS>>Write a function to find minimum of three numbers.
def min_of_three(a,b,c): 
      if (a <= b) and (a <= c): 
        smallest = a 
      elif (b <= a) and (b <= c): 
        smallest = b 
      else: 
        smallest = c 
      return smallest [/INST]assert min_of_three(10,20,0)==0
assert min_of_three(19,15,18)==15
assert min_of_three(-10,-20,-30)==-30</s>