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TST: Harden handling of Popen subprocesses #31503

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Merged
tacaswell merged 4 commits into from
Apr 16, 2026
Merged

TST: Harden handling of Popen subprocesses #31503

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c8b3e18
TST: Wrap _WaitForStringPopen in a context manager
QuLogic Apr 16, 2026
4890369
TST: Avoid hard-coded port in test_webagg
QuLogic Apr 16, 2026
6b5bc46
TST: Wrap urlopen in a context manager as well
QuLogic Apr 16, 2026
eebd854
TST: Tweak timeout setup in test_webagg
QuLogic Apr 16, 2026
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109 changes: 53 additions & 56 deletions lib/matplotlib/tests/test_backends_interactive.py
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Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,7 @@
import json
import os
import platform
import re
import signal
import subprocess
import sys
Expand All @@ -16,7 +17,6 @@

import pytest

import matplotlib as mpl
from matplotlib import _c_internal_utils
from matplotlib.backend_tools import ToolToggleBase
from matplotlib.testing import subprocess_run_helper as _run_helper, is_ci_environment
Expand Down Expand Up @@ -46,7 +46,7 @@ def wait_for(self, terminator):
f'Subprocess died before emitting expected {terminator!r}')
buf += c
if buf.endswith(terminator):
return
return buf


# Minimal smoke-testing of the backends for which the dependencies are
Expand Down Expand Up @@ -160,7 +160,6 @@ def _test_interactive_impl():
from matplotlib.backend_bases import KeyEvent, FigureCanvasBase
mpl.rcParams.update({
"webagg.open_in_browser": False,
"webagg.port_retries": 1,
})

mpl.rcParams.update(json.loads(sys.argv[1]))
Expand Down Expand Up @@ -484,32 +483,32 @@ def test_cross_Qt_imports(host, mpl):
@pytest.mark.skipif(sys.platform == "win32", reason="Cannot send SIGINT on Windows.")
def test_webagg():
pytest.importorskip("tornado")
proc = subprocess.Popen(
[sys.executable, "-c",
inspect.getsource(_test_interactive_impl)
+ "\n_test_interactive_impl()", "{}"],
env={**os.environ, "MPLBACKEND": "webagg", "SOURCE_DATE_EPOCH": "0"})
url = f'http://{mpl.rcParams["webagg.address"]}:{mpl.rcParams["webagg.port"]}'
timeout = time.perf_counter() + _test_timeout
try:
while True:
try:
retcode = proc.poll()
# check that the subprocess for the server is not dead
assert retcode is None
conn = urllib.request.urlopen(url)
break
except urllib.error.URLError:
if time.perf_counter() > timeout:
pytest.fail("Failed to connect to the webagg server.")
else:
continue
conn.close()
proc.send_signal(signal.SIGINT)
assert proc.wait(timeout=_test_timeout) == 0
finally:
if proc.poll() is None:
proc.kill()
source = (inspect.getsource(_test_interactive_impl) +
"\n_test_interactive_impl()")
rc = '{"backend": "webagg"}'
with _WaitForStringPopen([sys.executable, "-c", source, rc]) as proc:
try:
buf = proc.wait_for('Press Ctrl+C')
url = re.search(r'visit (https?:\/\/\S+)', buf).group(1)
timeout = time.perf_counter() + _test_timeout
while True:
try:
retcode = proc.poll()
# check that the subprocess for the server is not dead
assert retcode is None
with urllib.request.urlopen(url):
# Do nothing; we've just confirmed that we can connect.
break
except urllib.error.URLError:
if time.perf_counter() > timeout:
pytest.fail("Failed to connect to the webagg server.")
else:
continue
proc.send_signal(signal.SIGINT)
assert proc.wait(timeout=_test_timeout) == 0
finally:
if proc.poll() is None:
proc.kill()


def _lazy_headless():
Expand Down Expand Up @@ -737,18 +736,17 @@ def test_sigint(env, target, kwargs):
backend = env.get("MPLBACKEND")
if not backend.startswith(("qt", "macosx")):
pytest.skip("SIGINT currently only tested on qt and macosx")
proc = _WaitForStringPopen(
[sys.executable, "-c",
inspect.getsource(_test_sigint_impl) +
f"\n_test_sigint_impl({backend!r}, {target!r}, {kwargs!r})"])
try:
proc.wait_for('DRAW')
stdout, _ = proc.communicate(timeout=_test_timeout)
except Exception:
proc.kill()
stdout, _ = proc.communicate()
raise
assert 'SUCCESS' in stdout
source = (inspect.getsource(_test_sigint_impl) +
f"\n_test_sigint_impl({backend!r}, {target!r}, {kwargs!r})")
with _WaitForStringPopen([sys.executable, "-c", source]) as proc:
try:
proc.wait_for('DRAW')
stdout, _ = proc.communicate(timeout=_test_timeout)
except Exception:
proc.kill()
stdout, _ = proc.communicate()
raise
assert 'SUCCESS' in stdout


def _test_other_signal_before_sigint_impl(backend, target_name, kwargs):
Expand Down Expand Up @@ -796,20 +794,19 @@ def test_other_signal_before_sigint(env, target, kwargs, request):
# https://github.com/matplotlib/matplotlib/issues/27984
request.node.add_marker(
pytest.mark.xfail(reason="Qt backend is buggy on macOS"))
proc = _WaitForStringPopen(
[sys.executable, "-c",
inspect.getsource(_test_other_signal_before_sigint_impl) +
"\n_test_other_signal_before_sigint_impl("
f"{backend!r}, {target!r}, {kwargs!r})"])
try:
proc.wait_for('DRAW')
os.kill(proc.pid, signal.SIGUSR1)
proc.wait_for('SIGUSR1')
os.kill(proc.pid, signal.SIGINT)
stdout, _ = proc.communicate(timeout=_test_timeout)
except Exception:
proc.kill()
stdout, _ = proc.communicate()
raise
source = (inspect.getsource(_test_other_signal_before_sigint_impl) +
"\n_test_other_signal_before_sigint_impl("
f"{backend!r}, {target!r}, {kwargs!r})")
with _WaitForStringPopen([sys.executable, "-c", source]) as proc:
try:
proc.wait_for('DRAW')
os.kill(proc.pid, signal.SIGUSR1)
proc.wait_for('SIGUSR1')
os.kill(proc.pid, signal.SIGINT)
stdout, _ = proc.communicate(timeout=_test_timeout)
except Exception:
proc.kill()
stdout, _ = proc.communicate()
raise
print(stdout)
assert 'SUCCESS' in stdout
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