input: Write a function to calculate the square root of a user-defined positive number. If the input number is negative, raise a ValueError. The function should return the square root of the number.
  assert square_root(100)==10.0
  assert square_root(25)==5.0
  assert square_root(2)==1.4142135623730951
  try:
      square_root(-5)
  except ValueError:
      pass
  else:
      assert False, "Expected a ValueError"
  assert square_root(0)==0.0
output: def square_root(num):
      if num < 0:
          raise ValueError("Input number must be non-negative")
      return num ** 0.5