code: def func(self, xp, a):
      return xp.cos(a)
  
imports: import chainer
  import chainerx
  import chainerx.testing
  from chainerx_tests import dtype_utils
  from chainerx_tests import math_utils
  from chainerx_tests import op_utils
label_desc: Use image node_id 1 for calling the TestCos obj's underlying member method code with example usage: obj.func(xp, a) and returns: xp