Add github actions tests (pasteorg#77)

Borrowing the configuration from wsg-intercept and then editing
to fit so that we've got some automated tests.

To get this to work it was necessary to:

* adjust python versions
* update action version
* pin the ubuntu version
* fix warning in test_grantip
* form.cgi needs to not use six because it is not running in
   the virtualenv
* quiet deprecations in in form.cgi because cgi module is deprecated
* Skip the proxy test as it uses httpbin.org which is unreliable

.github/workflows/tests.yaml

@@ -0,0 +1,36 @@
+name: tests
+on: [push, workflow_dispatch]
+jobs:
+    build:
+        runs-on: ubuntu-20.04
+        strategy:
+            matrix:
+                include:
+                    - python: 2.7
+                      env: py27
+                    - python: 3.5
+                      env: py35
+                    - python: 3.6
+                      env: py36
+                    - python: 3.7
+                      env: py37
+                    - python: 3.8
+                      env: py38
+                    - python: 3.9
+                      env: py39
+                    - python: "3.10"
+                      env: py310
+                    - python: "3.11"
+                      env: py311
+                    - python: pypy-3.8
+                      env: pypy3
+        name: ${{ matrix.env }} on Python ${{ matrix.python }}
+        steps:
+        - uses: actions/checkout@v3
+        - uses: actions/setup-python@v3
+          with:
+              python-version: ${{ matrix.python }}
+        - run: pip install tox
+        - run: tox
+          env:
+            TOXENV: ${{ matrix.env }}

tests/cgiapp_data/form.cgi

@@ -2,13 +2,20 @@
 
 from __future__ import print_function
 
+import sys
+
+# Quiet warnings in this CGI so that it does not upset tests.
+if not sys.warnoptions:
+    import warnings
+    warnings.simplefilter("ignore")
+
+# TODO: cgi is deprecated and will go away in Python 3.13.
 import cgi
-import six
 
 print('Content-type: text/plain')
 print('')
 
-if six.PY3:
+if sys.version_info.major >= 3:
     # Python 3: cgi.FieldStorage keeps some field names as unicode and some as
     # the repr() of byte strings, duh.
 

tests/test_grantip.py

@@ -1,7 +1,7 @@
 from paste.auth import grantip
 from paste.fixture import *
 
-def test_make_app():
+def _make_app():
     def application(environ, start_response):
         start_response('200 OK', [('content-type', 'text/plain')])
         lines = [
@@ -23,7 +23,7 @@ def application(environ, start_response):
     return app
 
 def test_req():
-    app = test_make_app()
+    app = _make_app()
     def doit(remote_addr):
         res = app.get('/', extra_environ={'REMOTE_ADDR': remote_addr})
         return res.body

tests/test_proxy.py

@@ -1,6 +1,11 @@
+import pytest
+
 from paste import proxy
 from paste.fixture import TestApp
 
+# TODO: Skipping this for now as it is unreliable. Ideally we'd run something
+# locally and not have to rely on external stuff.
+@pytest.mark.skip(reason="httpbin.org is too slow these days")
 def test_proxy_to_website():
     # Not the most robust test...
     # need to test things like POSTing to pages, and getting from pages