infra: unit testing `check_package_version` (#16825)

Wrote a unit test for `check_package_version` in the core package.

Note that this is a revival of
https://github.com/langchain-ai/langchain/pull/16387 after GitHub
incident (see
https://github.com/langchain-ai/langchain/discussions/16796).

libs/core/tests/unit_tests/utils/test_utils.py

@@ -0,0 +1,30 @@
+from typing import Dict, Optional, Tuple, Type
+from unittest.mock import patch
+
+import pytest
+
+from langchain_core.utils import check_package_version
+
+
+@pytest.mark.parametrize(
+    ("package", "check_kwargs", "actual_version", "expected"),
+    [
+        ("stub", {"gt_version": "0.1"}, "0.1.2", None),
+        ("stub", {"gt_version": "0.1.2"}, "0.1.12", None),
+        ("stub", {"gt_version": "0.1.2"}, "0.1.2", (ValueError, "> 0.1.2")),
+        ("stub", {"gte_version": "0.1"}, "0.1.2", None),
+        ("stub", {"gte_version": "0.1.2"}, "0.1.2", None),
+    ],
+)
+def test_check_package_version(
+    package: str,
+    check_kwargs: Dict[str, Optional[str]],
+    actual_version: str,
+    expected: Optional[Tuple[Type[Exception], str]],
+) -> None:
+    with patch("langchain_core.utils.utils.version", return_value=actual_version):
+        if expected is None:
+            check_package_version(package, **check_kwargs)
+        else:
+            with pytest.raises(expected[0], match=expected[1]):
+                check_package_version(package, **check_kwargs)