chore(db_engine_specs): clean up column spec logic and add tests (#22871)

tests/unit_tests/db_engine_specs/test_bigquery.py

@@ -18,12 +18,18 @@
 # pylint: disable=line-too-long, import-outside-toplevel, protected-access, invalid-name
 
 import json
+from datetime import datetime
+from typing import Optional
 
+import pytest
 from pytest_mock import MockFixture
 from sqlalchemy import select
 from sqlalchemy.sql import sqltypes
 from sqlalchemy_bigquery import BigQueryDialect
 
+from tests.unit_tests.db_engine_specs.utils import assert_convert_dttm
+from tests.unit_tests.fixtures.common import dttm
+
 
 def test_get_fields() -> None:
     """
@@ -285,3 +291,24 @@ def test_parse_error_raises_exception() -> None:
         == expected_result
     )
     assert str(BigQueryEngineSpec.parse_error_exception(Exception(message_2))) == "6"
+
+
+@pytest.mark.parametrize(
+    "target_type,expected_result",
+    [
+        ("Date", "CAST('2019-01-02' AS DATE)"),
+        ("DateTime", "CAST('2019-01-02T03:04:05.678900' AS DATETIME)"),
+        ("TimeStamp", "CAST('2019-01-02T03:04:05.678900' AS TIMESTAMP)"),
+        ("Time", "CAST('03:04:05.678900' AS TIME)"),
+        ("UnknownType", None),
+    ],
+)
+def test_convert_dttm(
+    target_type: str, expected_result: Optional[str], dttm: datetime
+) -> None:
+    """
+    DB Eng Specs (bigquery): Test conversion to date time
+    """
+    from superset.db_engine_specs.bigquery import BigQueryEngineSpec as spec
+
+    assert_convert_dttm(spec, target_type, expected_result, dttm)