Test Windows, macOS and Linux on GitHub Actions (#1085)

.github/workflows/test.yml

@@ -0,0 +1,30 @@
+name: Test
+
+on: [push, pull_request]
+
+jobs:
+  build:
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        python-version: [3.6, 3.7]
+        os: [ubuntu-latest, macOS-latest, windows-latest]
+
+    steps:
+      - uses: actions/checkout@v1
+
+      - name: Set up Python ${{ matrix.python-version }}
+        uses: actions/setup-python@v1
+        with:
+          python-version: ${{ matrix.python-version }}
+
+      - name: Install dependencies
+        run: |
+          python -m pip install --upgrade pip
+          python -m pip install --upgrade coverage
+          python -m pip install -e ".[d]"
+
+      - name: Unit tests
+        run: |
+          coverage run tests/test_black.py