deps: Updates deprecation warning to FutureWarning re: 3.7 and 3.8

Author: chalmerlowe

db_dtypes/__init__.py

@@ -347,16 +347,22 @@ def __sub__(self, other):
         return super().__sub__(other)
 
 
-sys_major, sys_minor, sys_micro = _versions_helpers.extract_runtime_version()
-if sys_major == 3 and sys_minor in (7, 8):
-    warnings.warn(
-        "The python-bigquery library will stop supporting Python 3.7 "
-        "and Python 3.8 in a future major release expected in Q4 2024. "
-        f"Your Python version is {sys_major}.{sys_minor}.{sys_micro}. We "
-        "recommend that you update soon to ensure ongoing support. For "
-        "more details, see: [Google Cloud Client Libraries Supported Python Versions policy](https://cloud.google.com/python/docs/supported-python-versions)",
-        PendingDeprecationWarning,
-    )
+def _check_python_version():
+    """Checks the runtime Python version and issues a warning if needed."""
+    sys_major, sys_minor, sys_micro = _versions_helpers.extract_runtime_version()
+    if sys_major == 3 and sys_minor in (7, 8):
+        warnings.warn(
+            "The python-bigquery library as well as the python-db-dtypes-pandas library no "
+            "longer supports Python 3.7 and Python 3.8. "
+            f"Your Python version is {sys_major}.{sys_minor}.{sys_micro}. We "
+            "recommend that you update soon to ensure ongoing support. For "
+            "more details, see: [Google Cloud Client Libraries Supported Python Versions policy](https://cloud.google.com/python/docs/supported-python-versions)",
+            FutureWarning,
+            stacklevel=2,  # Point warning to the caller of __init__
+        )
+
+
+_check_python_version()
 
 
 if not JSONArray or not JSONDtype:

tests/unit/test__init__.py

@@ -0,0 +1,85 @@
+# Copyright 2025 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from unittest import mock
+
+import pytest
+
+# Module paths used for mocking
+MODULE_PATH = "db_dtypes"
+HELPER_MODULE_PATH = f"{MODULE_PATH}._versions_helpers"
+MOCK_EXTRACT_VERSION = f"{HELPER_MODULE_PATH}.extract_runtime_version"
+MOCK_WARN = "warnings.warn"  # Target the standard warnings module
+
+
+@pytest.mark.parametrize(
+    "mock_version_tuple, version_str",
+    [
+        ((3, 7, 10), "3.7.10"),
+        ((3, 7, 0), "3.7.0"),
+        ((3, 8, 5), "3.8.5"),
+        ((3, 8, 12), "3.8.12"),
+    ],
+)
+def test_check_python_version_warns_on_unsupported(mock_version_tuple, version_str):
+    """
+    Test that _check_python_version issues a FutureWarning for Python 3.7/3.8.
+    """
+
+    from db_dtypes import _check_python_version
+
+    # Mock the helper function it calls and the warnings.warn function
+    with mock.patch(MOCK_EXTRACT_VERSION, return_value=mock_version_tuple), mock.patch(
+        MOCK_WARN
+    ) as mock_warn_call:
+        _check_python_version()  # Call the function
+
+        # Assert that warnings.warn was called exactly once
+        mock_warn_call.assert_called_once()
+
+        # Check the arguments passed to warnings.warn
+        args, kwargs = mock_warn_call.call_args
+        assert len(args) >= 1  # Should have at least the message
+        warning_message = args[0]
+        warning_category = args[1] if len(args) > 1 else kwargs.get("category")
+
+        # Verify message content and category
+        assert "longer supports Python 3.7 and Python 3.8" in warning_message
+        assert warning_category == FutureWarning
+
+
+@pytest.mark.parametrize(
+    "mock_version_tuple",
+    [
+        (3, 9, 1),
+        (3, 10, 0),
+        (3, 11, 2),
+        (3, 12, 0),
+    ],
+)
+def test_check_python_version_does_not_warn_on_supported(mock_version_tuple):
+    """
+    Test that _check_python_version does NOT issue a warning for other versions.
+    """
+
+    from db_dtypes import _check_python_version
+
+    # Mock the helper function it calls and the warnings.warn function
+    with mock.patch(MOCK_EXTRACT_VERSION, return_value=mock_version_tuple), mock.patch(
+        MOCK_WARN
+    ) as mock_warn_call:
+        _check_python_version()
+
+        # Assert that warnings.warn was NOT called
+        mock_warn_call.assert_not_called()