docstr: DB Eng Specs (postgres): Test no grain expr lower case
docstr_tok: ["DB","Eng","Specs","(","postgres",")",":","Test","no","grain","expr","lower","case"]
code: def test_time_ex_lowr_col_no_grain(self):
      """
      DB Eng Specs (postgres): Test no grain expr lower case
      """
      col = column("lower_case")
      expr = PostgresEngineSpec.get_timestamp_expr(col, None, None)
      result = str(expr.compile(None, dialect=postgresql.dialect()))
      self.assertEqual(result, "lower_case")
  
imports: from textwrap import dedent
  from unittest import mock
  from flask.ctx import AppContext
  from sqlalchemy import column, literal_column
  from sqlalchemy.dialects import postgresql
  from superset.db_engine_specs import load_engine_specs
  from superset.db_engine_specs.postgres import PostgresEngineSpec
  from superset.errors import ErrorLevel, SupersetError, SupersetErrorType
  from superset.models.sql_lab import Query
  from superset.utils.database import get_example_database
  from tests.integration_tests.db_engine_specs.base_tests import TestDbEngineSpec
  from tests.integration_tests.fixtures.certificates import ssl_certificate
  from tests.integration_tests.fixtures.database import default_db_extra
label_desc: Use image node_id 4 for calling the TestPostgresDbEngineSpec obj's underlying member method code with example usage: obj.test_time_ex_lowr_col_no_grain() without return types