code: def check_basic(self):
      x = self.link.xp.asarray(self.x)
  
      expects = {}
      expects["l1"] = self.l1(x)
      expects["f1"] = self.f1(expects["l1"])
      expects["f2"] = self.f2(expects["f1"])
      expects["l2"] = self.l2(expects["f2"])
  
      self.check_call(x, expects)
  
imports: import numpy
  import unittest
  import chainer
  from chainer.backends.cuda import to_cpu
  from chainer.function import Function
  from chainer import testing
  from chainer.testing import attr
  from chainercv.links import PickableSequentialChain
  from chainercv.utils.testing import ConstantStubLink
label_desc: Use image node_id 6 for calling the PickableSequentialChainTestBase obj's underlying member method code with example usage: obj.check_basic() without return types