Manage unit tests in tox

.gitignore

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+.tox
+.stestr/
+__pycache__

.stestr.conf

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+[DEFAULT]
+test_path=./unit_tests
+top_dir=./

test-requirements.txt

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+# Lint and unit test requirements
+flake8
+stestr>=2.2.0
+mock>=1.2
+coverage>=3.6
+# Install netifaces as its a horrible charmhelpers lazy import
+netifaces
+charmhelpers
+git+https://github.com/canonical/operator.git#egg=ops

tox.ini

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+[tox]
+skipsdist = True
+envlist = pep8,py36
+# NOTE(beisner): Avoid build/test env pollution by not enabling sitepackages.
+sitepackages = False
+# NOTE(beisner): Avoid false positives by not skipping missing interpreters.
+skip_missing_interpreters = False
+
+[testenv]
+setenv = VIRTUAL_ENV={envdir}
+         PYTHONHASHSEED=0
+         TERM=linux
+install_command =
+  pip install {opts} {packages}
+
+[testenv:py35]
+basepython = python3
+deps = -r{toxinidir}/test-requirements.txt
+commands = stestr run {posargs}
+
+[testenv:py36]
+basepython = python3.6
+deps = -r{toxinidir}/test-requirements.txt
+commands = stestr run {posargs}
+
+[testenv:py37]
+basepython = python3.7
+deps = -r{toxinidir}/test-requirements.txt
+commands = stestr run {posargs}
+
+[testenv:py38]
+basepython = python3.8
+deps = -r{toxinidir}/test-requirements.txt
+commands = stestr run {posargs}
+
+[testenv:pep8]
+basepython = python3
+deps = -r{toxinidir}/test-requirements.txt
+commands = flake8 {posargs} . unit_tests
+
+[testenv:cover]
+# Technique based heavily upon
+# https://github.com/openstack/nova/blob/master/tox.ini
+basepython = python3
+deps = -r{toxinidir}/test-requirements.txt
+setenv =
+    {[testenv]setenv}
+    PYTHON=coverage run
+commands =
+    coverage erase
+    stestr run {posargs}
+    coverage combine
+    coverage html -d cover
+    coverage xml -o cover/coverage.xml
+    coverage report
+
+[coverage:run]
+branch = True
+concurrency = multiprocessing
+parallel = True
+source =
+    .
+omit =
+    .tox/*
+    */charmhelpers/*
+    unit_tests/*
+
+[testenv:venv]
+basepython = python3
+commands = {posargs}
+
+[flake8]
+# E402 ignore necessary for path append before sys module import in actions
+ignore = E402