Refactor xargs blocked sysconf test for clarity

- Add module-level docstring
- Extract subprocess script into helper function
- Add constant for blocked sysconf error message
- Improve test docstring explaining two-phase approach
- Add inline comments clarifying test orchestration
- Remove TODO comments

tests/xargs_with_blocked_sysconf_test.py

@@ -1,3 +1,4 @@
+"""Tests for pre_commit.xargs when os.sysconf is blocked in a sandbox environment."""
 from __future__ import annotations
 
 import subprocess
@@ -6,27 +7,19 @@ import textwrap
 
 # flake8: noqa: E501
 
-
-# TODO
-# import module without throwing exception
-# create object without throwing exception
-#  -- explicit _length
-#  -- implicit _length
+# Error message when os.sysconf is blocked in the test subprocess
+BLOCKED_SYSCONF_ERROR = 'blocked'
 
 
-def test_import_module_without_throwing_exception_as_subprocess() -> None:
-    """Import pre_commit.xargs in a subprocess even when os.sysconf is blocked.
+def _create_import_test_script() -> str:
+    """Create a Python script that tests importing pre_commit.xargs with blocked os.sysconf.
 
-    This test runs in a fresh subprocess where we can control os.sysconf
-    BEFORE any imports happen, avoiding the conftest.py chicken/egg problem.
-
-    With the current buggy implementation, this subprocess will crash
-    (returncode != 0) because os.sysconf('SC_ARG_MAX') is called at import
-    time and raises OSError.
-
-    After the fix, the subprocess should succeed (returncode == 0).
+    This script must run in a subprocess (not in the main pytest process) because:
+    1. We need to patch os.sysconf BEFORE any imports happen
+    2. conftest.py already imports pre_commit.xargs in the main process
+    3. A subprocess gives us a clean import state to test against
     """
-    script = textwrap.dedent("""
+    return textwrap.dedent(f"""
         import importlib
         import os
         from unittest import mock
@@ -36,7 +29,7 @@ def test_import_module_without_throwing_exception_as_subprocess() -> None:
             os.name = 'posix'
 
             # Block os.sysconf so that any SC_ARG_MAX lookup fails with OSError.
-            with mock.patch.object(os, 'sysconf', side_effect=OSError('blocked')):
+            with mock.patch.object(os, 'sysconf', side_effect=OSError('{BLOCKED_SYSCONF_ERROR}')):
                 # This should NOT raise with the fixed implementation.
                 importlib.import_module('pre_commit.xargs')
 
@@ -44,6 +37,21 @@ def test_import_module_without_throwing_exception_as_subprocess() -> None:
             main()
     """)
 
+
+def test_import_module_without_throwing_exception_as_subprocess() -> None:
+    """Test that pre_commit.xargs can be imported when os.sysconf is blocked.
+
+    This test uses a subprocess to avoid the conftest.py chicken/egg problem:
+    - Phase 1 (this function): Sets up and runs a subprocess with blocked os.sysconf
+    - Phase 2 (subprocess script): Attempts to import pre_commit.xargs in that environment
+
+    With the current buggy implementation, the subprocess crashes because os.sysconf
+    is called at import time. After the fix, the subprocess should succeed.
+    """
+    # Create the test script that will run in a subprocess
+    script = _create_import_test_script()
+
+    # Run the script in a fresh subprocess where we control os.sysconf
     proc = subprocess.run(
         [sys.executable, '-c', script],
         capture_output=True,
@@ -51,6 +59,7 @@ def test_import_module_without_throwing_exception_as_subprocess() -> None:
         cwd='/Users/michael/repos/pre-commit',
     )
 
+    # Assert the subprocess succeeded (import worked without exception)
     # Test-first: This test FAILS with current buggy behavior (subprocess crashes).
     # After fix, subprocess should succeed (returncode == 0).
     assert proc.returncode == 0, (