code: def get_revision(self):
      result = self.connection.execute(version_table.select())
      rows = result.fetchall()
      if len(rows) == 0:
          return None
      eq_(len(rows), 1)
      return rows[0]["version_num"]
  
imports: from sqlalchemy import Column
  from sqlalchemy import inspect
  from sqlalchemy import MetaData
  from sqlalchemy import String
  from sqlalchemy import Table
  from alembic import migration
  from alembic.testing import assert_raises
  from alembic.testing import assert_raises_message
  from alembic.testing import config
  from alembic.testing import eq_
  from alembic.testing import mock
  from alembic.testing.fixtures import TestBase
  from alembic.util import CommandError
label_desc: Use image node_id 5 for calling the TestMigrationContext obj's underlying member method code with example usage: obj.get_revision() and returns: rows, None