code: def test_get_timestamp_expression(self):
      tbl = self.get_table(name="birth_names")
      ds_col = tbl.get_column("ds")
      sqla_literal = ds_col.get_timestamp_expression(None)
      assert str(sqla_literal.compile()) == "ds"
  
      sqla_literal = ds_col.get_timestamp_expression("P1D")
      compiled = f"{sqla_literal.compile()}"
      if tbl.database.backend == "mysql":
          assert compiled == "DATE(ds)"
  
      prev_ds_expr = ds_col.expression
      ds_col.expression = "DATE_ADD(ds, 1)"
      sqla_literal = ds_col.get_timestamp_expression("P1D")
      compiled = f"{sqla_literal.compile()}"
      if tbl.database.backend == "mysql":
          assert compiled == "DATE(DATE_ADD(ds, 1))"
      ds_col.expression = prev_ds_expr
  
imports: import json
  from superset.utils.core import DatasourceType
  import textwrap
  import unittest
  from unittest import mock
  from superset import security_manager
  from superset.connectors.sqla.models import SqlaTable
  from superset.exceptions import SupersetException
  from superset.utils.core import override_user
  from tests.integration_tests.fixtures.birth_names_dashboard import load_birth_names_dashboard_with_slices, load_birth_names_data
  import pytest
  from sqlalchemy.engine.url import make_url
  from sqlalchemy.types import DateTime
  import tests.integration_tests.test_app
  from superset import app, db
  from superset.db_engine_specs.postgres import PostgresEngineSpec
  from superset.common.db_query_status import QueryStatus
  from superset.models.core import Database
  from superset.models.slice import Slice
  from superset.utils.database import get_example_database
  from .base_tests import SupersetTestCase
  from .fixtures.energy_dashboard import load_energy_table_with_slice, load_energy_table_data
label_desc: Use image node_id 1 for calling the TestSqlaTableModel obj's underlying member method code with example usage: obj.test_get_timestamp_expression() without return types