From 85beb0c2ac3cbcb39695172e228d4c4054d41c34 Mon Sep 17 00:00:00 2001
From: Nick <wrignj08@gmail.com>
Date: Thu, 2 Jul 2026 12:46:43 +0800
Subject: [PATCH] ci: run tests in parallel with pytest-xdist

Add pytest-xdist to the dev group and enable parallel test execution.

- Local default: `-n auto --dist worksteal` in pytest.ini, so `pytest`
  fans out across all cores (worksteal rebalances the heavy Water-sweep
  and fuzz tests). Full suite ~76s -> ~51s locally.
- CI: `-n 2` overrides the auto default. GitHub runners have 4 vCPUs and
  some tests spawn smoothify's own worker pool, so a smaller fan-out
  avoids oversubscribing the runner.
- README: note the parallel default and `-n 0` to serialise for debugging.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
---
 .github/workflows/ci.yml | 7 +++++--
 README.md                | 8 ++++----
 pyproject.toml           | 3 ++-
 pytest.ini               | 2 ++
 4 files changed, 13 insertions(+), 7 deletions(-)

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index d0c7679..2a455fb 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -33,8 +33,11 @@ jobs:
         run: uv run mypy smoothify/
 
       - name: Test
-        run: uv run pytest tests/ -x -q
+        # -n 2 overrides the local `-n auto` default: GitHub runners have 4
+        # vCPUs and some tests spawn smoothify's own worker pool, so a smaller
+        # fan-out avoids oversubscribing the runner.
+        run: uv run pytest tests/ -n 2 -x -q
 
       - name: Notebook smoke test
         if: matrix.python-version == '3.11'
-        run: uv run pytest --nbmake examples/*.ipynb -q
+        run: uv run pytest --nbmake examples/*.ipynb -n 2 -q
diff --git a/README.md b/README.md
index 86d1ebf..ce5fade 100644
--- a/README.md
+++ b/README.md
@@ -244,17 +244,17 @@ Smoothify uses [pytest](https://pytest.org/). After cloning the repository, inst
 # Install dependencies (including the dev group)
 uv sync
 
-# Run all tests
+# Run all tests (parallelised across CPU cores by default via pytest-xdist)
 uv run pytest tests/
 
 # Run with coverage
 uv run pytest tests/ --cov=smoothify --cov-report=html
 
-# Run a single test
-uv run pytest tests/test_chaikin.py::TestChaikinCornerCutting::test_simple_square_polygon
+# Run a single test (add `-n 0` to disable parallelism for clearer output)
+uv run pytest tests/test_chaikin.py::TestChaikinCornerCutting::test_simple_square_polygon -n 0
 ```
 
-If you prefer not to use uv, install the dev dependencies into your environment and run `pytest tests/` directly.
+The suite runs in parallel by default (`-n auto` in `pytest.ini`); pass `-n 0` to run serially when debugging. If you prefer not to use uv, install the dev dependencies into your environment and run `pytest tests/` directly.
 
 ## Contributing
 
diff --git a/pyproject.toml b/pyproject.toml
index 0ce6697..fdee1f5 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -49,6 +49,7 @@ dev = [
     "pre-commit>=4.0",
     "pytest>=8.4.2",
     "pytest-cov>=6.0.0",
+    "pytest-xdist>=3.8.0",
     "ruff>=0.12.2",
 ]
 
@@ -77,4 +78,4 @@ select = ["E", "F", "B"]
 
 [tool.ruff.lint.per-file-ignores]
 "tests/*" = ["E402"]
-"*.ipynb" = ["E402", "E501"]
\ No newline at end of file
+"*.ipynb" = ["E402", "E501"]
diff --git a/pytest.ini b/pytest.ini
index 6ce1475..a97ab4d 100644
--- a/pytest.ini
+++ b/pytest.ini
@@ -9,6 +9,8 @@ addopts =
     --strict-markers
     --tb=short
     --color=yes
+    -n auto
+    --dist worksteal
 markers =
     slow: marks tests as slow (deselect with '-m "not slow"')
     integration: marks tests as integration tests