added pytest github action

.github/workflows/run_tests.yml

+name: Run Tests
+
+on: [pull_request]
+
+jobs:
+  tests:
+    runs-on: ubuntu-latest
+
+    strategy:
+      matrix:
+        python-version: [3.6, 3.7, 3.8, 3.9]
+
+    steps:
+      - uses: actions/checkout@v2
+      - name: Set up Python ${{ matrix.python-version }}
+        uses: actions/setup-python@v2
+        with:
+          python-version: ${{ matrix.python-version }}
+
+    - name: install deps
+      run: |
+        python3 -m pip install -U pip
+        python3 -m pip install --editable .[dev]
+
+    - name: run pytest
+      run: pytest