Run tests on MacOS, Windows and PyPy

Author: dolfinus

.github/workflows/test.yml

@@ -32,7 +32,13 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        python-version: ['2.7', '3.5', '3.6', '3.7', '3.8', '3.9', '3.10']
+        python-version: ['2.7', '3.5', '3.6', '3.7', '3.8', '3.9', '3.10', pypy-2.7, pypy-3.7, pypy-3.8]
+        os: [ubuntu-18.04]
+        include:
+        - os: macos-latest
+          python-version: '3.10'
+        - os: windows-latest
+          python-version: '3.10'
 
     steps:
     - name: Checkout code