input: Write a function to print a pattern of asterisks that starts with an increasing triangle and then a decreasing triangle. Implement the function in Python and provide example usage with assertions.
  
  assert print_pattern()==None
output: def print_pattern():
      for i in range(1, 6):
          print('*' * i)
      for i in range(4, 0, -1):
          print('*' * i)