def METHOD_NAME(self):
    self.obj_a.distance_criteria = ["var_1", "var_2", "var_3"]
    self.obj_b.distance_criteria = ["var_1", "var_2", "var_3"]
    self.obj_c.distance_criteria = ["var_5"]
    self.obj_a.var_1, self.obj_a.var_2, self.obj_a.var_3 = [0.1], [1, 2], [2.1]
    self.obj_b.var_1, self.obj_b.var_2, self.obj_b.var_3 = [1.8], [0, 0.1], [1.1]
    self.assertEqual(self.obj_a.distance(self.obj_b), 1.9)
    # change the length of a attribute list
    self.obj_b.var_1, self.obj_b.var_2, self.obj_b.var_3 = [1.8], [0, 0, 0.1], [1.1]
    self.assertEqual(self.obj_a.distance(self.obj_b), 1.7)
    # sanity check
    self.assertEqual(self.obj_b.distance(self.obj_b), 0.0)