Flush stdout and stderr in pytester.run (pytest-dev#13695)

Attempted to make `test_faulthandler.py::test_timeout` more reliable on CI, but ultimately this was not accomplished.

However, it seems flushing `stdout` and `stderr` during `pytester.run` seems the right thing to do, so it was decided to leave the calls and only skip the test in more specific scenarios that were failing frequently on CI (see pytest-dev#13695 for discussion history).

We should extend the skip list as needed.

Follow-up on pytest-dev#13684.
Partially addresses pytest-dev#7022.

Author: ogrisel

changelog/13695.contrib.rst

@@ -0,0 +1 @@
+Flush `stdout` and `stderr` in `Pytester.run` to avoid truncated outputs in `test_faulthandler.py::test_timeout` on CI -- by :user:`ogrisel`.

src/_pytest/pytester.py

@@ -1422,7 +1422,6 @@ def run(
                 stdin=stdin,
                 stdout=f1,
                 stderr=f2,
-                close_fds=(sys.platform != "win32"),
             )
             if popen.stdin is not None:
                 popen.stdin.close()
@@ -1443,6 +1442,8 @@ def handle_timeout() -> None:
                     ret = popen.wait(timeout)
                 except subprocess.TimeoutExpired:
                     handle_timeout()
+            f1.flush()
+            f2.flush()
 
         with p1.open(encoding="utf8") as f1, p2.open(encoding="utf8") as f2:
             out = f1.read().splitlines()

testing/test_faulthandler.py

@@ -2,6 +2,7 @@
 from __future__ import annotations
 
 import io
+import os
 import sys
 
 from _pytest.pytester import Pytester
@@ -76,7 +77,13 @@ def test_disabled():
     "enabled",
     [
         pytest.param(
-            True, marks=pytest.mark.skip(reason="sometimes crashes on CI (#7022)")
+            True,
+            marks=pytest.mark.skipif(
+                "CI" in os.environ
+                and sys.platform == "linux"
+                and sys.version_info >= (3, 14),
+                reason="sometimes crashes on CI because of truncated outputs (#7022)",
+            ),
         ),
         False,
     ],

testing/test_terminal.py

@@ -2250,8 +2250,8 @@ def test_times_multiline(
         output.stdout.re_match_lines(
             [
                 r"test_bar.py ...................",
-                r"........... \s+ \d{1,3}[\.[a-z\ ]{1,2}\d{0,3}\w{1,2}$",
-                r"test_foo.py \.{5} \s+ \d{1,3}[\.[a-z\ ]{1,2}\d{0,3}\w{1,2}$",
+                r"........... \s+ \d{1,4}[\.[a-z\ ]{1,2}\d{0,3}\w{1,2}$",
+                r"test_foo.py \.{5} \s+ \d{1,4}[\.[a-z\ ]{1,2}\d{0,3}\w{1,2}$",
             ],
             consecutive=True,
         )