Add regular and stress tests for CliRunner stream lifecycle and ownership

Closes: pallets#824, pallets#3110
Reverts: pallets#2991
Reproduces pallets#2993
Supersed: pallets#3140

Author: kdeldycke

.github/workflows/tests.yaml

@@ -32,6 +32,25 @@ jobs:
         with:
           python-version: ${{ matrix.python }}
       - run: uv run --locked tox run -e ${{ matrix.tox || format('py{0}', matrix.python) }}
+  stress:
+    name: stress (${{ matrix.name || matrix.python }})
+    runs-on: ${{ matrix.os || 'ubuntu-latest' }}
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - {python: '3.14'}
+          - {name: free-threaded, python: '3.14t', tox: stress-py3.14t}
+    steps:
+      - uses: actions/checkout@93cb6efe18208431cddfb8368fd83d5badbf9bfd # v5.0.1
+      - uses: astral-sh/setup-uv@5a7eac68fb9809dea845d802897dc5c723910fa3 # v7.1.3
+        with:
+          enable-cache: true
+          prune-cache: false
+      - uses: actions/setup-python@e797f83bcb11b83ae66e0230d6156d7c80228e7c # v6.0.0
+        with:
+          python-version: ${{ matrix.python }}
+      - run: uv run --locked tox run -e ${{ matrix.tox || format('stress-py{0}', matrix.python) }}
   typing:
     runs-on: ubuntu-latest
     steps:

CHANGES.rst

@@ -7,7 +7,11 @@ Unreleased
 -   Hide ``Sentinel.UNSET`` values as ``None`` when using ``lookup_default()``.
     :issue:`3136` :pr:`3199` :pr:`3202` :pr:`3209` :pr:`3212` :pr:`3224`
 -   Prevent ``_NamedTextIOWrapper`` from closing streams owned by ``StreamMixer``.
-    :issue:`824` :issue:`2993` :pr:`3139`
+    :issue:`824` :issue:`2991` :issue:`2993` :issue:`3110` :pr:`3139` :pr:`3140`
+-   Add comprehensive tests for ``CliRunner`` stream lifecycle, covering
+    logging interaction, multi-threaded safety, and sequential invocation
+    isolation. Add high-iteration stress tests behind a ``stress`` marker
+    with a dedicated CI job. :pr:`3139`
 
 Version 8.3.1
 --------------

pyproject.toml

@@ -83,6 +83,10 @@ testpaths = ["tests"]
 filterwarnings = [
     "error",
 ]
+markers = [
+    "stress: high-iteration stress tests for race conditions (deselect with '-m \"not stress\"')",
+]
+addopts = "-m 'not stress'"
 
 [tool.coverage.run]
 branch = true
@@ -142,6 +146,7 @@ env_list = [
     "py3.14", "py3.13", "py3.12", "py3.11", "py3.10",
     "py3.14t",
     "pypy3.11",
+    "stress-py3.14", "stress-py3.14t",
     "style",
     "typing",
     "docs",
@@ -160,6 +165,16 @@ commands = [[
     {replace = "posargs", default = [], extend = true},
 ]]
 
+[tool.tox.env.stress]
+description = "stress tests for stream lifecycle race conditions"
+commands = [[
+    "pytest", "-v", "--tb=short", "-x", "-m", "stress",
+    "--basetemp={env_tmp_dir}",
+    "--override-ini=addopts=",
+    "tests/test_stream_lifecycle.py",
+    {replace = "posargs", default = [], extend = true},
+]]
+
 [tool.tox.env.style]
 description = "run all pre-commit hooks on all files"
 dependency_groups = ["pre-commit"]