ci: run the unit tests, which nothing was running (#257)

main_test.py has 99 tests and CI never executed a single one. The repo's
workflows are commit-check (self test), pre-commit (black, mypy,
codespell, yaml/toml), release and used-by — none of them invoke pytest.
Every release so far shipped with the suite unrun outside contributors'
machines.

Matrix is the floor and the newest across the three OSes the action
supports. 3.10 is the real floor: main.py annotates with `str | None`
without `from __future__ import annotations`, so the annotation is
evaluated at def time, and main_test.py uses parenthesized context
managers — both 3.10+.

Installs requirements.txt rather than the bare deps, so the commit-check
version under test is the one the action ships, which is also the version
the golden tests read back out of importlib.metadata.

Verified from a clean venv: the exact install and pytest invocation this
workflow runs gives 99 passed, 2 subtests passed.


Claude-Session: https://claude.ai/code/session_01U9zFxq8V4qxG4aMzJhGBFn

Co-authored-by: Claude Opus 5 <noreply@anthropic.com>

Author: shenxianpeng

.github/workflows/test.yml

@@ -0,0 +1,43 @@
+name: Test
+
+permissions:
+  contents: read
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+
+jobs:
+  test:
+    strategy:
+      fail-fast: false
+      matrix:
+        # The floor and the newest. 3.10 is the real floor: main.py annotates
+        # with `str | None` and has no `from __future__ import annotations`, so
+        # the annotation is evaluated at def time, and main_test.py uses
+        # parenthesized context managers. Both are 3.10+.
+        #
+        # The action itself runs on whatever python3 the runner ships, so the
+        # in-between versions add little here — unlike commit-check, which is a
+        # published package and tests every one.
+        py: ['3.10', '3.14']
+        os: ['ubuntu-latest', 'macos-latest', 'windows-latest']
+    runs-on: ${{ matrix.os }}
+    steps:
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+      - uses: actions/setup-python@5fda3b95a4ea91299a34e894583c3862153e4b97 # v7.0.0
+        with:
+          python-version: ${{ matrix.py }}
+
+      - name: Install dependencies
+        run: |
+          python -m pip install --upgrade pip
+          # requirements.txt rather than a bare install: it pins the same
+          # commit-check the action ships, which is the version the golden
+          # tests expect to read back out of importlib.metadata.
+          python -m pip install -r requirements.txt pytest
+
+      - name: Run unit tests
+        run: python -m pytest main_test.py -v