code: def testStructSubstraction(self):
      s1 = schema.Struct(
          ("a", schema.Scalar()),
          ("b", schema.Scalar()),
          ("c", schema.Scalar()),
      )
      s2 = schema.Struct(("b", schema.Scalar()))
      s = s1 - s2
      self.assertEqual(["a", "c"], s.field_names())
  
      s3 = schema.Struct(("a", schema.Scalar()))
      s = s1 - s3
      self.assertEqual(["b", "c"], s.field_names())
  
      with self.assertRaises(TypeError):
          s1 - schema.Scalar()
  
imports: from caffe2.python import core, schema
  import numpy
  import unittest
  import pickle
  import random
label_desc: Use image node_id 16 for calling the TestDB obj's underlying member method code with example usage: obj.testStructSubstraction() without return types