code: def test_alter_column_nullable_w_existing_type(self):
      context = op_fixture("oracle")
      op.alter_column("t", "c", nullable=True, existing_type=Integer)
      context.assert_("ALTER TABLE t MODIFY c NULL")
  
imports: import sqlalchemy
  from sqlalchemy import Column
  from sqlalchemy import exc
  from sqlalchemy import Integer
  from sqlalchemy import MetaData
  from sqlalchemy import Table
  from alembic import command
  from alembic import op
  from alembic.testing import assert_raises_message
  from alembic.testing import combinations
  from alembic.testing import config
  from alembic.testing import eq_
  from alembic.testing import is_true
  from alembic.testing.env import _no_sql_testing_config
  from alembic.testing.env import clear_staging_env
  from alembic.testing.env import staging_env
  from alembic.testing.env import three_rev_fixture
  from alembic.testing.fixtures import capture_context_buffer
  from alembic.testing.fixtures import op_fixture
  from alembic.testing.fixtures import TestBase
  from alembic.testing.suite._autogen_fixtures import AutogenFixtureTest
  from alembic.util import sqla_compat
label_desc: Use image node_id 18 for calling the OpTest obj's underlying member method code with example usage: obj.test_alter_column_nullable_w_existing_type() without return types