From 8edd931f98d082b982b5919da146021bbafcb049 Mon Sep 17 00:00:00 2001
From: Sanchit Rishi <sharmasanchitrishi@gmail.com>
Date: Tue, 3 Feb 2026 19:32:57 +0530
Subject: [PATCH] verification

---
 lib/matplotlib/tests/conftest.py | 42 ++++++++++++++++++++++++++++++++
 1 file changed, 42 insertions(+)

diff --git a/lib/matplotlib/tests/conftest.py b/lib/matplotlib/tests/conftest.py
index 6afd566750e9..e144a48e5039 100644
--- a/lib/matplotlib/tests/conftest.py
+++ b/lib/matplotlib/tests/conftest.py
@@ -1,2 +1,44 @@
 from matplotlib.testing.conftest import (  # noqa
     mpl_test_settings, pytest_configure, pytest_unconfigure, pd, text_placeholders, xr)
+import sys
+import os
+import pytest
+
+def pytest_collection_modifyitems(config, items):
+    """
+    On Windows CI, force tests that spawn fresh Python processes to run serially.
+
+    Rationale:
+    Tests that spawn a new Python process (via sys.executable) compete for
+    Desktop Heap / Handles on Windows. Running them in parallel causes
+    resource exhaustion and timeouts.
+    """
+    # 1. Only apply on Windows
+    if sys.platform != "win32":
+        return
+
+    # 2. Only apply on CI (let local devs run fast)
+    if not os.environ.get("CI"):
+        return
+
+    # 3. The Specific "Python Spawning" Files
+    # Identified via static analysis of `sys.executable` usage.
+    serial_files = {
+        'test_backends_interactive.py',
+        'test_backend_webagg.py',
+        'test_basic.py',
+        'test_determinism.py',
+        'test_font_manager.py',
+        'test_matplotlib.py',
+        'test_preprocess_data.py',
+        'test_pyplot.py',
+        'test_rcparams.py',
+        'test_sphinxext.py',
+        'test_texmanager.py',
+    }
+
+    # 4. Apply the Single Group (Strict Serialization)
+    for item in items:
+        # Check if the test belongs to one of the identified files
+        if any(f in str(item.fspath) for f in serial_files):
+            item.add_marker(pytest.mark.xdist_group(name="serial_python_spawn"))
\ No newline at end of file