test: add unit tests for start_date validation

Co-Authored-By: AJ Steers <aj@airbyte.io>

Author: devin-ai-integration[bot]

unit_tests/sources/file_based/config/test_abstract_file_based_spec.py

@@ -7,7 +7,9 @@
 import pytest
 from jsonschema import ValidationError, validate
 from pydantic.v1 import BaseModel
+from pydantic.v1 import ValidationError as PydanticValidationError
 
+from airbyte_cdk.sources.file_based.config.abstract_file_based_spec import AbstractFileBasedSpec
 from airbyte_cdk.sources.file_based.config.file_based_stream_config import (
     AvroFormat,
     CsvFormat,
@@ -40,3 +42,28 @@ def test_parquet_file_type_is_not_a_valid_csv_file_type(
             validate(instance=format_config[file_type], schema=file_format.schema())
     else:
         validate(instance=format_config[file_type], schema=file_format.schema())
+
+
+@pytest.mark.parametrize(
+    "start_date, should_pass",
+    [
+        pytest.param("2021-01-01T00:00:00.000000Z", True, id="with_microseconds"),
+        pytest.param("2021-01-01T00:00:00Z", True, id="without_microseconds"),
+        pytest.param("2021-01-01T00:00:00.000Z", True, id="with_milliseconds"),
+        pytest.param("2025-01-01T00:00:00Z", True, id="terraform_provider_format"),
+        pytest.param("2021-01-01T00:00:00+00:00", True, id="with_timezone_offset"),
+        pytest.param("2021-01-01", True, id="date_only"),
+        pytest.param(None, True, id="none_value"),
+        pytest.param("not-a-date", False, id="invalid_string"),
+        pytest.param("2021/01/01", True, id="slash_separator_also_accepted"),
+        pytest.param("", False, id="empty_string"),
+    ],
+)
+def test_start_date_validation(start_date: str, should_pass: bool) -> None:
+    """Test that start_date accepts various valid ISO8601/RFC3339 formats."""
+    if should_pass:
+        result = AbstractFileBasedSpec.validate_start_date(start_date)
+        assert result == start_date
+    else:
+        with pytest.raises(ValueError, match="is not a valid datetime string"):
+            AbstractFileBasedSpec.validate_start_date(start_date)