code: def _assert_alter_col(self, m1, m2, pk, nullable=None):
      ops = self._fixture(m1, m2, return_ops=True)
      modify_table = ops.ops[-1]
      alter_col = modify_table.ops[0]
  
      if nullable is None:
          eq_(alter_col.existing_nullable, not pk)
      else:
          eq_(alter_col.existing_nullable, nullable)
      assert alter_col.existing_type._compare_type_affinity(Integer())
      return alter_col
  
imports: from sqlalchemy import BigInteger
  from sqlalchemy import Column
  from sqlalchemy import Integer
  from sqlalchemy import MetaData
  from sqlalchemy import Table
  from sqlalchemy.testing import in_
  from ._autogen_fixtures import AutogenFixtureTest
  from ...None import testing
  from ...testing import config
  from ...testing import eq_
  from ...testing import is_
  from ...testing import TestBase
label_desc: Use image node_id 5 for calling the AlterColumnTest obj's underlying member method code with example usage: obj._assert_alter_col(m1, m2, pk, nullable) and returns: alter_col