code: def setUp(self):
      self.x1 = numpy.random.uniform(-10.0, 10.0, self.shape).astype(
          self.dtype
      )
      self.x2 = numpy.random.uniform(-10.0, 10.0, self.shape).astype(
          self.dtype
      )
      self.gy = numpy.random.uniform(-1, 1, self.shape).astype(
          self.dtype
      )
      self.ggx1 = numpy.random.uniform(-10.0, 10.0, self.shape).astype(
          self.dtype
      )
      self.ggx2 = numpy.random.uniform(-10.0, 10.0, self.shape).astype(
          self.dtype
      )
      if self.dtype == numpy.float16:
          self.backward_options = {
              "eps": 1e-3,
              "atol": 2**-4,
              "rtol": 2**-4,
          }
          self.double_backward_options = {
              "eps": 1e-3,
              "atol": 2**-4,
              "rtol": 2**-4,
          }
      else:
          self.backward_options = {"atol": 1e-3, "rtol": 1e-3}
          self.double_backward_options = {"atol": 1e-3, "rtol": 1e-3}
  
      # Avoid non-differentiable point
      self.x1[(abs(self.x1) < 1e-2) & (self.x2 < 0)] = 1
      self.ggx1[(abs(self.ggx1) < 1e-2) & (self.ggx2 < 0)] = 1
  
imports: import unittest
  import numpy
  import chainer
  from chainer.backends import cuda
  import chainer.functions
  from chainer import gradient_check
  from chainer import testing
  from chainer.testing import attr
label_desc: Use image node_id 1 for calling the TestArctan2 obj's underlying member method code with example usage: obj.setUp() without return types