add github actions workflows

.github/workflows/tests.yml

@@ -0,0 +1,56 @@
+name: Tests
+
+on: [push, pull_request]
+
+jobs:
+  test:
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        os: ["windows-latest", "ubuntu-latest", "macos-latest"]
+        python-version: ["3.7", "3.8", "3.9"]
+
+    env:
+      PYTHON_VERSION: ${{ matrix.python-version }}
+      PARALLEL: "true"
+      COVERAGE: "true"
+
+    steps:
+      - name: Check out repository code
+        uses: actions/checkout@v2
+
+      # Setup Python (faster than using Python container)
+      - name: Setup Python
+        uses: actions/setup-python@v2
+        with:
+          python-version: ${{ matrix.python-version }}
+
+      - name: Install poetry
+        uses: snok/install-poetry@v1
+        with:
+          virtualenvs-create: true
+          virtualenvs-in-project: true
+          installer-parallel: true
+
+      - name: Load cached venv
+        id: cached-poetry-dependencies
+        uses: actions/cache@v2
+        with:
+          path: .venv
+          key: venv-${{ runner.os }}-${{ hashFiles('**/poetry.lock') }}
+
+      - name: Install dependencies
+        if: steps.cache-poetry.outputs.cache-hit != 'true'
+        run: |
+          poetry install --no-interaction --no-root
+
+      - name: Install library
+        run: |
+          poetry install --no-interaction
+
+      - name: Run tests
+        shell: bash -l {0}
+        run: |
+          source .venv/bin/activate
+          pytest tests/