input: Write a function to calculate the running total of numbers in a given list using numpy. The function should return an array where each element is the cumulative sum of the elements up to that index in the input list. The function should be named runningTotal and should accept a single parameter arr which is the input list. If the input list is empty, the function should return an empty list.
  
  assert np.array_equal(runningTotal([1, 2, 3, 4]), np.array([1, 3, 6, 10]))
  assert np.array_equal(runningTotal([5, 3, 1]), np.array([5, 8, 9]))
  assert np.array_equal(runningTotal([]), np.array([]))
  assert np.array_equal(runningTotal([-1, -2, -3]), np.array([-1, -3, -6]))
  assert np.array_equal(runningTotal([10]), np.array([10]))
output: import numpy as np
  
  def runningTotal(arr):
      if not arr:
          return np.array([])
      return np.cumsum(arr)