input: Write a function to return an array with the running total of numbers in a given list using numpy. If the input array is empty, return an empty array.
  
  import numpy as np
  
  def runningTotal(arr):
      if len(arr) == 0:
          return np.array([])
      return np.cumsum(arr)
  
  assert np.array_equal(runningTotal([1, 2, 3, 4]), np.array([1, 3, 6, 10]))==True
  assert np.array_equal(runningTotal([5, 3, -1, 4]), np.array([5, 8, 7, 11]))==True
  assert np.array_equal(runningTotal([0, 0, 0]), np.array([0, 0, 0]))==True
  assert np.array_equal(runningTotal([10]), np.array([10]))==True
  assert np.array_equal(runningTotal([]), np.array([]))==True
output: if len(arr) == 0:
      return np.array([])
  return np.cumsum(arr)