code: def check_forward(self, x_data):
      # In chainer, update will be like x.array -= lr * x.grad,
      # which means negative gradients will increase values.
  
      # Not exceeding
      range_max = x_data + 0.1
      range_min = x_data - 0.1
      x = chainer.Variable(x_data)
      y = invert_gradients(x, range_min=range_min, range_max=range_max)
  
      loss = functions.sum(y)  # Minimize y
      loss.backward()
      self.assertTrue((x.grad > 0).all())  # Decrease x
      x.cleargrad()
  
      loss = -functions.sum(y)  # Maximize y
      loss.backward()
      self.assertTrue((x.grad < 0).all())  # Increase x
      x.cleargrad()
  
      # Exceeding range_max
      range_max = x_data - 0.1
      range_min = x_data - 0.2
      y = invert_gradients(x, range_min=range_min, range_max=range_max)
  
      loss = functions.sum(y)  # Minimize y
      loss.backward()
      self.assertTrue((x.grad > 0).all())  # Decrease x
      x.cleargrad()
  
      loss = -functions.sum(y)  # Maximize y
      loss.backward()
      self.assertTrue((x.grad > 0).all())  # Decrease x
      x.cleargrad()
  
      # Exceeding range_min
      range_max = x_data + 0.2
      range_min = x_data + 0.1
      y = invert_gradients(x, range_min=range_min, range_max=range_max)
  
      loss = functions.sum(y)  # Minimize y
      loss.backward()
      self.assertTrue((x.grad < 0).all())  # Increase x
      x.cleargrad()
  
      loss = -functions.sum(y)  # Maximize y
      loss.backward()
      self.assertTrue((x.grad < 0).all())  # Increase x
      x.cleargrad()
  
file_path: chainerrl/tests/functions_tests/test_invert_gradients.py
imports: import unittest
  import chainer
  from chainer import cuda
  from chainer import functions
  from chainer import testing
  from chainer.testing import attr
  from chainer.testing import condition
  import numpy
  from chainerrl.functions.invert_gradients import invert_gradients
label_desc: Use image node_id 2 for calling the TestInvertGradients obj's underlying member method code with example usage: obj.check_forward(x_data) without return types