Add tox tests & coveralls github action

This commit essentially adds back tests to our CI pipeline. They were
previously dropped due to Travis pricing policy change.

This workflow utilizes a few interesting projects to make this action
easier to maintain such as the coveralls github action
(https://github.com/marketplace/actions/coveralls-github-action)
and the tox-gh-actions project
(https://github.com/ymyzk/tox-gh-actions)

.github/workflows/tests.yml

@@ -0,0 +1,43 @@
+name: Tox tests and Coveralls
+on: [push, pull_request]
+jobs:
+    run_tests:
+        runs-on: ubuntu-latest
+        strategy:
+            fail-fast: false
+            matrix:
+                python-version: [3.6, 3.7, 3.8, 3.9, pypy-3.7]
+
+        steps:
+            - name: Checkout repository
+              uses: actions/checkout@v2
+
+            - name: Set up Python ${{ matrix.python-version }}
+              uses: actions/setup-python@v2
+              with:
+                  python-version: ${{ matrix.python-version }}
+
+            - name: Install dependencies
+              run: |
+                  python -m pip install --upgrade pip
+                  pip install tox tox-gh-actions
+
+            - name: Test with tox
+              run: tox
+
+            - name: Coveralls Parallel
+              uses: coverallsapp/github-action@master
+              with:
+                  github-token: ${{ secrets.github_token }}
+                  flag-name: run-${{ matrix.python-version }}
+                  parallel: true
+
+    coverage_report:
+        needs: run_tests
+        runs-on: ubuntu-latest
+        steps:
+            - name: Compile and submit coveralls report
+              uses: coverallsapp/github-action@master
+              with:
+                  github-token: ${{ secrets.github_token }}
+                  parallel-finished: true

tox.ini

@@ -1,6 +1,14 @@
 [tox]
 envlist = py36, py37, py38, py39, pypy3, flake8
 
+[gh-actions]
+python =
+    3.6: py36
+    3.7: py37
+    3.8: py38
+    3.9: py39
+    pypy-3: pypy3
+
 [testenv]
 setenv =
     PYTHONPATH = {toxinidir}:{toxinidir}/pipreqs