DOC: add explanatory comments

tacaswell · timhoffm · web-flow · commit b3e03afe84dc · 2022-03-23T11:22:37.000-04:00
Co-authored-by: Tim Hoffmann &lt;2836374+timhoffm@users.noreply.github.com&gt;
diff --git a/lib/matplotlib/tests/test_backend_tk.py b/lib/matplotlib/tests/test_backend_tk.py
@@ -26,6 +26,7 @@ def _isolated_tk_test(success_count, func=None):
         return functools.partial(_isolated_tk_test, success_count)
 
     if "MPL_TEST_ESCAPE_HATCH" in os.environ:
+        # set in subprocess_run_helper() below
         return func
 
     @pytest.mark.skipif(
