Action to run tests and upload coverage to codecov.io

Closes #843.

.github/workflows/test-coverage.yml

@@ -0,0 +1,41 @@
+name: Calculate test coverage
+
+on:
+  push:
+    branches:
+      - master
+  pull_request:
+    branches:
+      - master
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    steps:
+    - name: Check out datasette
+      uses: actions/checkout@v2
+    - name: Set up Python
+      uses: actions/setup-python@v1
+      with:
+        python-version: 3.8
+    - uses: actions/cache@v2
+      name: Configure pip caching
+      with:
+        path: ~/.cache/pip
+        key: ${{ runner.os }}-pip-${{ hashFiles('**/setup.py') }}
+        restore-keys: |
+          ${{ runner.os }}-pip-
+    - name: Install Python dependencies
+      run: |
+        python -m pip install -e .[test]
+        python -m pip install pytest-cov
+    - name: Run tests
+      run: |-
+        ls -lah
+        cat .coveragerc
+        pytest --cov=datasette --cov-config=.coveragerc --cov-report xml:coverage.xml --cov-report term
+        ls -lah
+    - name: Upload coverage report
+      uses: codecov/codecov-action@v1
+      with:
+        token: ${{ secrets.CODECOV_TOKEN }}
+        file: coverage.xml