'Test the copy function for AddExpresion class.'

def test_add_expr_copy(self):

    atom = (self.x + self.y)
    copy = atom.copy()
    self.assertTrue((type(copy) is type(atom)))
    self.assertEqual(copy.args, atom.args)
    self.assertFalse((copy.args is atom.args))
    self.assertEqual(copy.get_data(), atom.get_data())
    copy = atom.copy(args=[self.A, self.B])
    self.assertTrue((type(copy) is type(atom)))
    self.assertTrue((copy.args[0] is self.A))
    self.assertTrue((copy.args[1] is self.B))
    self.assertEqual(copy.get_data(), atom.get_data())
