Run contract tests under the right Python interpreter

[MrJoy]

run_contract_tests ran python3 from PATH and ignored environment.python_path. When that python3 has no pytest, a passing test file comes back as total=0, errors=0, which looks like nothing went wrong. The same file, run on this machine where PATH resolves python3 to pyenv's 3.9:

OLD default: 0 0 0 []      # total, passed, errors
NEW default: 1 1 0

Changes:

• Contract tests run under environment.python_path when one is set, and under sys.executable otherwise. EnvironmentSpec and resolve_environment now default to sys.executable too.
• Pact's own purelib is no longer added to PYTHONPATH. It came in with 29ed47d so anyio would be importable from the wrong interpreter. Under sys.executable it's redundant. Under a custom python_path it mixes two environments' site-packages, which is bad news for compiled packages like pydantic_core.
• No module named pytest now comes back as an environment error naming the interpreter, instead of 0/0.
• pytest moves from the dev extra to the runtime dependencies. The harness now runs pytest under pact's own interpreter, so a pipx or uv tool install with no extras needs it. Checked with a bare uv pip install . into a fresh venv: pytest 9.1.1 comes along, and the same test file reports 1 1 0. The No module named pytest error still covers a custom python_path that lacks it.

Tests: the 8 new and changed tests in test_test_harness.py and test_environment.py all fail against the old code. Full suite: 9 failed, 2371 passed, 2 skipped, and the 9 are exactly the ones #21 fixes.

🤖 Generated with Claude Code

https://claude.ai/code/session_011FeZUmAZbyQWDJNAPkUA3S

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[adaptcom]

Confidence Score: 0/5

Summary

Review of 35ed5b2 is stale because the PR advanced to 85cda5a. That commit addresses pytest packaging; rerun validation after fixing the remaining interpreter-configuration propagation issue.

Important Files Changed

File	Overview
src/pact/config.py	Defaults execution environments to Pact’s interpreter
src/pact/test_harness.py	Interpreter selection changes without propagating configuration from production callers
tests/test_environment.py	Updates default-interpreter expectations
tests/test_test_harness.py	Adds interpreter, PYTHONPATH isolation, and missing-pytest tests

↻ Re-run review · View in Adapt