[David Fowler (davidfowl)]

Description

Fixes #19542
Also fixes a latent hang in the helper's timeout path.

AddPythonAppTests.PythonResourceSupportsWithReference failed once on windows-latest (run 32375588350, job 96448944641) with Failed to create virtual environment. The test took 2m 06s, and the venv process wrote no stdout or stderr.

Root cause

• Unnecessary pip bootstrap. Every AddPythonAppTests test that uses CreateTempPythonProject runs a full python -m venv .venv and then pip install, under a fixed 2-minute deadline. Five of those tests only build the app model, and so does the failing one. They need .venv to exist because AddPythonApp adds a -venv-creator resource when it's missing. They never run pip. A full venv runs ensurepip, which starts a pip subprocess that installs and byte-compiles about 1,000 files. Without pip, venv creation copies about 5 files. On a cold Windows runner (Defender, MoUsoCoreWorker and svchost were busy in the heartbeat), this step exceeded 2 minutes. The heartbeat at 14:00:28, 75s into the wait, shows no python process among the top CPU consumers, so the process was blocked on I/O or the OS rather than computing.
• Timeout path waits for the process anyway. On timeout, the helper read stdout and stderr to EOF before calling Kill. A process that truly hung would therefore block the test until the 20-minute MTP hang timeout instead of failing at 2 minutes. That's why the failure reported 2m 06s: the read waited for python to exit.

Fix (test-only)

• CreateTempPythonProject(..., withPip: false) is the default for model-only tests. It creates the venv with python -m venv --without-pip .venv and skips pip install. The venv interpreter exists, so the resource model (command path, no venv-creator) is unchanged.
• Tests that actually run pip still bootstrap it. PythonResourceFinishesSuccessfully starts the app, and its installer resource runs .venv pip. The instrumented test installs requirements.
• Both process waits now kill on timeout before draining output.

No assertions were changed, and no retries or sleeps were added.

Evidence

Regression test: CreateTempPythonProject_ForModelOnlyTests_CreatesVirtualEnvironmentWithoutBootstrappingPip asserts that the model-only venv has an interpreter and no pip.

• Before, with main's -m venv .venv: fails, with Model-only test projects should not bootstrap pip, but found '/tmp/bBYQbR/.venv/bin/pip'.
• After: passes.

Per-test duration (TRX, Linux, Python 3.12), main → this PR:

Test	main	PR
PythonResourceSupportsWithReference (the flaky test)	2.51s	0.053s
AddPythonAppProducesDockerfileResourceInManifest	2.53s	0.037s
AddPythonApp_SetsResourcePropertiesCorrectly	2.65s	0.039s
AddPythonApp_ObsoleteMethod_StillWorks	2.50s	0.039s
AddPythonAppWithScriptArgs_IncludesTheArguments	2.50s	0.044s
PythonResourceFinishesSuccessfully (still uses pip; starts the app)	6.40s	9.75s (passes)
AddInstrumentedPythonProjectProducesDockerfileResourceInManifest (still uses pip)	9.12s	5.88s

Measured separately: python -m venv .venv writes 1,010 files in 4.27s, while --without-pip writes 5 files in 0.05s. Model-only tests no longer start an ensurepip/pip subprocess, which was the step that exceeded the deadline.

Recurrence: this is the only recorded occurrence. A scan of the last 300 ci.yml runs (2026-10-30 22:08 to 2026-10-31 06:15 UTC; the CI test selector skips Hosting.Python on most runs) found 0 failures in 20 Hosting.Python (windows-latest) jobs. On main, the Windows suite usually takes about 75s (for example, job 124463643298: 1m 15s). The failure is rare and depends on runner conditions, so the evidence above is the removed exposure rather than a local Windows repro.

Validation

• Aspire.Hosting.Python.Tests (full project, functional PythonResourceFinishesSuccessfully included, which starts the app via DCP): 119 passed, 0 skipped, 3 failed. The 3 failures are WithUv_GeneratesDockerfileInPublishMode* Verify snapshots. They fail identically on main in this environment because the run is as root and Verify scrubs /root/ to {UserProfile}. They're unrelated to this change, and CI is the authority.

Windows CI on this PR (job 124468350194): Hosting.Python (windows-latest) reported 122 succeeded, 0 failed, in 31.6s. On main this suite takes about 75s, so most of the Windows suite time was venv/pip bootstrap that model-only tests didn't need.

Checklist

• Is this feature complete?
  • Yes. Ready to ship.
• Are you including unit tests for the changes and scenario tests if relevant?
  • Yes
• Did you add public API?
  • No
• Does the change make any security assumptions or guarantees?
  • No

🤖 Posted by AspireAgent (AI Agent)

[github-actions]

🚀 Dogfood this PR with:

⚠️ WARNING: Do not do this without first carefully reviewing the code of this PR to satisfy yourself it is safe.

curl -fsSL https://raw.githubusercontent.com/microsoft/aspire/main/eng/scripts/get-aspire-cli-pr.sh | bash -s -- 21539

Or

• Run remotely in PowerShell:

iex "& { $(irm https://raw.githubusercontent.com/microsoft/aspire/main/eng/scripts/get-aspire-cli-pr.ps1) } 21539"

[github-actions]

Tests selector

1 / 100 PR test projects · 0 PR jobs, from 1 changed file.

Selected PR test projects (1 / 100)

Aspire.Hosting.Python.Tests

Selected PR jobs (0)

none

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How these were chosen — grouped by what changed

🧪 tests/Aspire.Hosting.Python.Tests/AddPythonAppTests.cs (changed test)
→ 1 directly: Aspire.Hosting.Python.Tests

Job reasons

none

---

Selection computed for commit 5895beb.

[Copilot]

🟢 Approval recommended

No active review issues block the test-only changes that skip unnecessary pip setup in model-only Python environments.

No open issues 🎉

What changed in this PR

Reduces exposure to the flaky Python virtual-environment timeout in #19542 by skipping unnecessary pip setup in Aspire’s model-only Python hosting tests. Changes are test-only.

Changes:

• Creates model-only virtual environments without pip, while preserving pip setup for tests that need it.
• Kills timed-out venv creation and package installation processes before draining their output.
• Adds a regression test verifying that model-only environments contain a Python interpreter but no pip executable.

File	Description
tests/​Aspire.Hosting.Python.Tests/​AddPythonAppTests.cs	Makes pip setup conditional, fixes timeout handling, and adds regression coverage.

_{Review effort: Balanced}

[aspire-repo-bot]

✅ No documentation update needed.

docs_optional → test_only. Triggered signal: pr_body_has_cli_flag_mention (evidence: PR body mentions python -m venv --without-pip .venv, which is the test helper's internal command, not an Aspire CLI flag). The only changed file is tests/Aspire.Hosting.Python.Tests/AddPythonAppTests.cs, which matches tests/**. No user-facing behavior changed.