text: import unittest
  from nodes import *
  import numpy as np
  from numpy.testing import *
  
  
  def numericalGradient(operation, input: Connection, output: Connection, mask = 1):
      dx = 1E-8
      operation.forward()
      operation.backward()
      x = output.value
      input.value += dx * mask
      operation.forward()
      operation.backward()
      xdx = output.value
      return (xdx - x) / dx * output.gradient
  