input: Write a function to calculate the running total of numbers in a given list using numpy. If the input list is empty, the function should return an empty list.
  import numpy as np
  
  def runningTotal(arr):
      if len(arr) == 0:
          return []
      return np.cumsum(arr)
  
  assert np.array_equal(runningTotal([1, 2, 3, 4]), [1, 3, 6, 10])
  assert np.array_equal(runningTotal([5, 3, 8, 1]), [5, 8, 16, 17])
  assert np.array_equal(runningTotal([]), [])
  assert np.array_equal(runningTotal([-1, 0, 1]), [-1, -1, 0])
output: if len(arr) == 0:
          return []
      return np.cumsum(arr)