matplotlib · jkseppan · Jul 5, 2025 · Jul 6, 2025
diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
@@ -337,9 +337,18 @@ jobs:
           if [[ "${{ matrix.python-version }}" == '3.13t' ]]; then
             export PYTHON_GIL=0
           fi
-          pytest -rfEsXR -n auto \
-            --maxfail=50 --timeout=300 --durations=25 \
-            --cov-report=xml --cov=lib --log-level=DEBUG --color=yes
+          FLAGS=(
+            -rfEsXR
+            --maxfail=50
+            --timeout=300
+            --durations=25
+            --cov-report=xml
+            --cov=lib
+            --log-level=DEBUG
+            --color=yes
+          )
+          pytest "${FLAGS[@]}" -m 'not subprocess' -n auto
+          pytest "${FLAGS[@]}" -m subprocess --cov-append
 
       - name: Cleanup non-failed image files
         if: failure()

diff --git a/azure-pipelines.yml b/azure-pipelines.yml
@@ -120,9 +120,18 @@ stages:
 
               echo "##vso[task.setvariable variable=VS_COVERAGE_TOOL]$TOOL"
 
-              PYTHONFAULTHANDLER=1 pytest -rfEsXR -n 2 \
-                  --maxfail=50 --timeout=300 --durations=25 \
-                  --junitxml=junit/test-results.xml --cov-report=xml --cov=lib
+              FLAGS=(
+                -rfEsXR
+                --maxfail=50
+                --timeout=300
+                --durations=25
+                --cov-report=xml
+                --cov=lib
+              )
+              PYTHONFAULTHANDLER=1 pytest "${FLAGS[@]}" -m 'not subprocess' -n 2 \
+                  --junitxml=junit/test-results-1.xml
+              PYTHONFAULTHANDLER=1 pytest "${FLAGS[@]}" -m subprocess \
+                  --junitxml=junit/test-results-2.xml --cov-append
 
               if [[ $VS_VER == 2022 ]]; then
                 "$TOOL" shutdown $SESSION_ID
@@ -153,7 +162,8 @@ stages:
 
           - task: PublishTestResults@2
             inputs:
-              testResultsFiles: '**/test-results.xml'
+              mergeTestResults: true
+              testResultsFiles: '**/test-results*.xml'
               testRunTitle: 'Python $(python.version)'
             condition: succeededOrFailed()
 

diff --git a/lib/matplotlib/testing/conftest.py b/lib/matplotlib/testing/conftest.py
@@ -15,6 +15,7 @@ def pytest_configure(config):
         ("markers", "backend: Set alternate Matplotlib backend temporarily."),
         ("markers", "baseline_images: Compare output against references."),
         ("markers", "pytz: Tests that require pytz to be installed."),
+        ("markers", "subprocess: Tests that start a subprocess."),
         ("filterwarnings", "error"),
         ("filterwarnings",
          "ignore:.*The py23 module has been deprecated:DeprecationWarning"),

diff --git a/lib/matplotlib/tests/test_backend_inline.py b/lib/matplotlib/tests/test_backend_inline.py
@@ -10,6 +10,7 @@
 pytest.importorskip('nbconvert')
 pytest.importorskip('ipykernel')
 pytest.importorskip('matplotlib_inline')
+pytestmark = pytest.mark.subprocess
 
 
 def test_ipynb():

diff --git a/lib/matplotlib/tests/test_backend_nbagg.py b/lib/matplotlib/tests/test_backend_nbagg.py
@@ -9,6 +9,7 @@
 nbformat = pytest.importorskip('nbformat')
 pytest.importorskip('nbconvert')
 pytest.importorskip('ipykernel')
+pytestmark = pytest.mark.subprocess
 
 # From https://blog.thedataincubator.com/2016/06/testing-jupyter-notebooks/
 

diff --git a/lib/matplotlib/tests/test_backend_webagg.py b/lib/matplotlib/tests/test_backend_webagg.py
@@ -6,6 +6,7 @@
 from matplotlib.testing import subprocess_run_for_testing
 
 
+@pytest.mark.subprocess
 @pytest.mark.parametrize("backend", ["webagg", "nbagg"])
 def test_webagg_fallback(backend):
     pytest.importorskip("tornado")

diff --git a/lib/matplotlib/tests/test_backends_interactive.py b/lib/matplotlib/tests/test_backends_interactive.py
@@ -22,6 +22,9 @@
 from matplotlib.testing import subprocess_run_helper as _run_helper, is_ci_environment
 
 
+pytestmark = pytest.mark.subprocess
+
+
 class _WaitForStringPopen(subprocess.Popen):
     """
     A Popen that passes flags that allow triggering KeyboardInterrupt.

diff --git a/lib/matplotlib/tests/test_basic.py b/lib/matplotlib/tests/test_basic.py
@@ -5,6 +5,8 @@
 
 from matplotlib.testing import subprocess_run_for_testing
 
+import pytest
+
 
 def test_simple():
     assert 1 + 1 == 2
@@ -28,6 +30,7 @@ def test_override_builtins():
     assert overridden <= ok_to_override
 
 
+@pytest.mark.subprocess
 def test_lazy_imports():
     source = textwrap.dedent("""
     import sys

diff --git a/lib/matplotlib/tests/test_determinism.py b/lib/matplotlib/tests/test_determinism.py
@@ -21,6 +21,8 @@
 from matplotlib.text import TextPath
 from matplotlib.transforms import IdentityTransform
 
+pytestmark = pytest.mark.subprocess
+
 
 def _save_figure(objects='mhip', fmt="pdf", usetex=False):
     mpl.use(fmt)

diff --git a/lib/matplotlib/tests/test_font_manager.py b/lib/matplotlib/tests/test_font_manager.py
@@ -288,6 +288,7 @@ def test_fontcache_thread_safe():
     subprocess_run_helper(_test_threading, timeout=10)
 
 
+@pytest.mark.subprocess
 def test_lockfilefailure(tmp_path):
     # The logic here:
     # 1. get a temp directory from pytest

diff --git a/lib/matplotlib/tests/test_matplotlib.py b/lib/matplotlib/tests/test_matplotlib.py
@@ -19,6 +19,7 @@ def test_parse_to_version_info(version_str, version_tuple):
     assert matplotlib._parse_to_version_info(version_str) == version_tuple
 
 
+@pytest.mark.subprocess
 @pytest.mark.skipif(sys.platform == "win32",
                     reason="chmod() doesn't work as is on Windows")
 @pytest.mark.skipif(sys.platform != "win32" and os.geteuid() == 0,
@@ -37,6 +38,7 @@ def test_tmpconfigdir_warning(tmp_path):
         os.chmod(tmp_path, mode)
 
 
+@pytest.mark.subprocess
 def test_importable_with_no_home(tmp_path):
     subprocess_run_for_testing(
         [sys.executable, "-c",

diff --git a/lib/matplotlib/tests/test_preprocess_data.py b/lib/matplotlib/tests/test_preprocess_data.py
@@ -245,6 +245,7 @@ def funcy(ax, x, y, z, t=None):
                          funcy.__doc__)
 
 
+@pytest.mark.subprocess
 def test_data_parameter_replacement():
     """
     Test that the docstring contains the correct *data* parameter stub

diff --git a/lib/matplotlib/tests/test_pyplot.py b/lib/matplotlib/tests/test_pyplot.py
@@ -12,6 +12,7 @@
 from matplotlib import pyplot as plt
 
 
+@pytest.mark.subprocess
 def test_pyplot_up_to_date(tmp_path):
     pytest.importorskip("black")
 

diff --git a/lib/matplotlib/tests/test_rcparams.py b/lib/matplotlib/tests/test_rcparams.py
@@ -528,6 +528,7 @@ def test_rcparams_reset_after_fail():
         assert mpl.rcParams['text.usetex'] is False
 
 
+@pytest.mark.subprocess
 @pytest.mark.skipif(sys.platform != "linux", reason="Linux only")
 def test_backend_fallback_headless_invalid_backend(tmp_path):
     env = {**os.environ,
@@ -545,6 +546,7 @@ def test_backend_fallback_headless_invalid_backend(tmp_path):
             env=env, check=True, stderr=subprocess.DEVNULL)
 
 
+@pytest.mark.subprocess
 @pytest.mark.skipif(sys.platform != "linux", reason="Linux only")
 def test_backend_fallback_headless_auto_backend(tmp_path):
     # specify a headless mpl environment, but request a graphical (tk) backend
@@ -567,6 +569,7 @@ def test_backend_fallback_headless_auto_backend(tmp_path):
     assert backend.strip().lower() == "agg"
 
 
+@pytest.mark.subprocess
 @pytest.mark.skipif(
     sys.platform == "linux" and not _c_internal_utils.xdisplay_is_valid(),
     reason="headless")

diff --git a/lib/matplotlib/tests/test_sphinxext.py b/lib/matplotlib/tests/test_sphinxext.py
@@ -16,6 +16,7 @@
 tinypages = Path(__file__).parent / 'data/tinypages'
 
 
+@pytest.mark.subprocess
 def build_sphinx_html(source_dir, doctree_dir, html_dir, extra_args=None):
     # Build the pages with warnings turned into errors
     extra_args = [] if extra_args is None else extra_args

diff --git a/lib/matplotlib/tests/test_texmanager.py b/lib/matplotlib/tests/test_texmanager.py
@@ -63,6 +63,7 @@ def test_unicode_characters():
         fig.canvas.draw()
 
 
+@pytest.mark.subprocess
 @needs_usetex
 def test_openin_any_paranoid():
     completed = subprocess_run_for_testing(