Add a github actions workflow to run unit tests.

.github/workflows/main.yaml

@@ -0,0 +1,53 @@
+# main test workflow
+
+name: main
+
+on:
+  schedule:
+    - cron:  '* * * * 5'   # Runs on every Friday.
+  push:
+    branches: [ '*', $default-branch ]
+    tags: ['[0-9]*']   # anything looks like a version.
+  pull_request:
+    branches: [ $default-branch ]
+
+jobs:
+  build:
+    runs-on: ${{ matrix.os }}
+
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ ubuntu-latest, macos-latest, windows-latest ]
+        python-version: [ 3.9 ]
+        include:
+          - {deploy: true, os: ubuntu-latest, python-version: 3.9 }
+    steps:
+
+    - name: Checkout source code
+      uses: actions/checkout@v2
+
+    - name: setup python
+      uses: actions/setup-python@v2
+      with:
+        python-version: ${{ matrix.python-version }}
+
+    - name: Setup test env
+      run: |
+        python -m pip install tox-gh
+
+    - name: Python Unit tests
+      run: |
+        tox4
+
+    - name: Build Python sdist
+      if: startsWith(github.ref, 'refs/tags') && matrix.deploy
+      run: |
+        python setup.py sdist
+
+    # TODO: Release to pypi.
+    - name: Publish distribution to PyPI
+      uses: pypa/gh-action-pypi-publish@master
+      if: startsWith(github.ref, 'refs/tags') && matrix.deploy
+      with:
+        password: ${{ secrets.PYPI_SECRET }}