First pass at integration support on Python 3.

src/allmydata/util/_python3.py

@@ -23,6 +23,9 @@ if PY2:
     from future.builtins import filter, map, zip, ascii, chr, hex, input, next, oct, open, pow, round, super, bytes, dict, list, object, range, str, max, min  # noqa: F401
 
 
+# Every time a module is added here, also add it to tox.ini environment
+# integrations3. Bit of duplication, but it's only a handful of files so quite
+# temporary.
 PORTED_INTEGRATION_TESTS = [
     "integration.test_servers_of_happiness",
 ]

tox.ini

@@ -7,7 +7,7 @@
 [gh-actions]
 python =
     2.7: py27-coverage,codechecks
-    3.6: py36-coverage
+    3.6: py36-coverage,integration3
     3.7: py37-coverage
     3.8: py38-coverage
     3.9: py39-coverage,typechecks,codechecks3
@@ -97,6 +97,17 @@ commands =
          coverage report
 
 
+[testenv:integration3]
+basepython = python3
+setenv =
+         COVERAGE_PROCESS_START=.coveragerc
+commands =
+         # NOTE: 'run with "py.test --keep-tempdir -s -v integration/" to debug failures'
+         py.test --timeout=1800 --coverage -v {posargs:integration/test_servers_of_happiness.py}
+         coverage combine
+         coverage report
+
+
 [testenv:codechecks]
 basepython = python2.7
 # On macOS, git inside of towncrier needs $HOME.