input: Write a function to calculate the running total of numbers in a given list using numpy. Return an array with the running total. If the input list is empty, return an empty array.
  import numpy as np
  
  def runningTotal(arr):
      return np.cumsum(arr)
  
  assert np.array_equal(runningTotal([1, 2, 3, 4]), np.array([1, 3, 6, 10]))
  assert np.array_equal(runningTotal([5, 4, 3, 2, 1]), np.array([5, 9, 12, 14, 15]))
  assert np.array_equal(runningTotal([7, 7, 7, 7]), np.array([7, 14, 21, 28]))
  assert np.array_equal(runningTotal([10]), np.array([10]))
  assert np.array_equal(runningTotal([]), np.array([]))
output: import numpy as np
  
  def runningTotal(arr):
      return np.cumsum(arr)