new_contents: import pytest
  from plenum.common.types import Commit
  from collections import OrderedDict
  from plenum.common.messages.fields import NonNegativeNumberField
  
  EXPECTED_ORDERED_FIELDS = ["instId", "viewNo", "ppSeqNo"]
  EXPECTED_ORDERED_VALIDATORS = [NonNegativeNumberField,
                                 NonNegativeNumberField,
                                 NonNegativeNumberField]
  
  
  def test_hash_expected_type():
      assert Commit.typename == "COMMIT"
  
  
  def test_has_expected_fields():
      actual_field_names = list(OrderedDict(Commit.schema).keys())
      assert actual_field_names == EXPECTED_ORDERED_FIELDS
  
  
  def test_has_expected_validators():
      schema = dict(Commit.schema)
      for field, validator in zip(EXPECTED_ORDERED_FIELDS,
                                  EXPECTED_ORDERED_VALIDATORS):
          assert isinstance(schema[field], validator)
  
subject: add test for commit message