ci: enable github test workflow

.github/workflows/test.yaml

@@ -0,0 +1,88 @@
+name: Tests
+
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+    types:
+      - opened
+      - synchronize
+
+concurrency:
+  group: tests-${{ github.head_ref || github.ref }}
+  cancel-in-progress: ${{ github.event_name == 'pull_request' }}
+
+jobs:
+  tests:
+    name: ${{ matrix.os }} / ${{ matrix.python-version }}
+    runs-on: ${{ matrix.image }}
+    strategy:
+      matrix:
+        os: [Ubuntu, macOS, Windows]
+        python-version: ["3.7", "3.8", "3.9", "3.10", "3.11"]
+        include:
+          - os: Ubuntu
+            image: ubuntu-22.04
+          - os: Windows
+            image: windows-2022
+          - os: macOS
+            image: macos-12
+      fail-fast: false
+    defaults:
+      run:
+        shell: bash
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set up Python ${{ matrix.python-version }}
+        uses: actions/setup-python@v5
+        id: setup-python
+        with:
+          python-version: ${{ matrix.python-version }}
+
+      - name: Install and configure Poetry
+        uses: snok/install-poetry@v1
+        with:
+          version: 1.7.1
+          virtualenvs-in-project: true
+
+      - name: Set up cache
+        uses: actions/cache@v4
+        id: cache
+        with:
+          path: .venv
+          key: venv-${{ runner.os }}-${{ steps.setup-python.outputs.python-version }}-${{ hashFiles('**/poetry.lock') }}
+
+      - name: Ensure cache is healthy
+        if: steps.cache.outputs.cache-hit == 'true'
+        run: |
+          # `timeout` is not available on macOS, so we define a custom function.
+          [ "$(command -v timeout)" ] || function timeout() { perl -e 'alarm shift; exec @ARGV' "$@"; }
+
+          # Using `timeout` is a safeguard against the Poetry command hanging for some reason.
+          timeout 10s poetry run pip --version || rm -rf .venv
+
+      - name: Check lock file
+        run: poetry check --lock
+
+      - name: Install dependencies
+        run: poetry install
+
+      - run: mkdir coverage
+
+      - name: Run pytest
+        run: poetry run coverage run -m pytest -v
+        env:
+          COVERAGE_FILE: coverage/.coverage.${{ runner.os }}-py${{ matrix.python-version }}
+          CONTEXT: ${{ runner.os }}-py${{ matrix.python-version }}
+
+      - name: Store coverage files
+        uses: actions/upload-artifact@v3
+        with:
+          name: coverage
+          path: coverage
+
+      - name: Check for clean working tree
+        run: |
+          git diff --exit-code --stat HEAD