code: def test_negative_margin(self):
      self.margin = -1
      self.assertRaises(
          ValueError, self.check_forward, self.a, self.p, self.n
      )
      self.assertRaises(
          ValueError,
          self.check_backward,
          self.a,
          self.p,
          self.n,
          self.gy,
      )
  
imports: import unittest
  import numpy
  import six
  import chainer
  from chainer.backends import cuda
  from chainer import functions
  from chainer import gradient_check
  from chainer import testing
  from chainer.testing import attr
label_desc: Use image node_id 3 for calling the TestTriplet obj's underlying member method code with example usage: obj.test_negative_margin() without return types