input: Write a function to return an array with the running total of numbers in a given list using numpy. If the given list 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]), [1, 3, 6, 10])
  assert np.array_equal(runningTotal([3, 2, 5, 7]), [3, 5, 10, 17])
  assert np.array_equal(runningTotal([]), [])
  assert np.array_equal(runningTotal([5, -1, 0, 2]), [5, 4, 4, 6])
  assert np.array_equal(runningTotal([10]), [10])
output: def runningTotal(arr):
      if len(arr) == 0:
          return np.array([])
      return np.cumsum(arr)