input: Write a python function to print a pattern of stars.
  assert pattern(3) == None  # Expected pattern:
  # *
  # * *
  # * * *
  assert pattern(4) == None  # Expected pattern:
  # *
  # * *
  # * * *
  # * * * *
  assert pattern(2) == None  # Expected pattern:
  # *
  # * *
output: def pattern(n):
      for i in range(1, n + 1):
          print('* ' * i)