On NetBSD with python-3.4.2 I see the following issue when running the tests for py-flake8-2.2.5:

running build_ext
test_get_parser (flake8.tests.test_engine.TestEngine) ... ok
test_get_python_version (flake8.tests.test_engine.TestEngine) ... ok
test_get_style_guide (flake8.tests.test_engine.TestEngine) ... ok
test_get_style_guide_kwargs (flake8.tests.test_engine.TestEngine) ... ok
test_register_extensions (flake8.tests.test_engine.TestEngine) ... ok
test_stdin_disables_jobs (flake8.tests.test_engine.TestEngine) ... ok
test_windows_disables_jobs (flake8.tests.test_engine.TestEngine) ... ok
Traceback (most recent call last):
  File "setup.py", line 74, in <module>
    test_suite='nose.collector',
  File "/usr/pkg/lib/python3.4/distutils/core.py", line 148, in setup
    dist.run_commands()
  File "/usr/pkg/lib/python3.4/distutils/dist.py", line 955, in run_commands
    self.run_command(cmd)
  File "/usr/pkg/lib/python3.4/distutils/dist.py", line 974, in run_command
    cmd_obj.run()
  File "/usr/pkg/lib/python3.4/site-packages/setuptools/command/test.py", line 142, in run
    self.with_project_on_sys_path(self.run_tests)
  File "/usr/pkg/lib/python3.4/site-packages/setuptools/command/test.py", line 122, in with_project_on_sys_path
    func()
  File "/usr/pkg/lib/python3.4/site-packages/setuptools/command/test.py", line 163, in run_tests
    testRunner=self._resolve_as_ep(self.test_runner),
  File "/usr/pkg/lib/python3.4/unittest/main.py", line 93, in __init__
    self.runTests()
  File "/usr/pkg/lib/python3.4/unittest/main.py", line 244, in runTests
    self.result = testRunner.run(self.test)
  File "/usr/pkg/lib/python3.4/unittest/runner.py", line 168, in run
    test(result)
  File "/usr/pkg/lib/python3.4/unittest/suite.py", line 87, in __call__
    return self.run(*args, **kwds)
  File "/usr/pkg/lib/python3.4/unittest/suite.py", line 130, in run
    self._removeTestAtIndex(index)
  File "/usr/pkg/lib/python3.4/unittest/suite.py", line 83, in _removeTestAtIndex
    self._removed_tests += test.countTestCases()
  File "/usr/pkg/lib/python3.4/unittest/suite.py", line 41, in countTestCases
    cases = self._removed_tests
AttributeError: 'FinalizingSuiteWrapper' object has no attribute '_removed_tests'
*** Error code 1


I have reported this

https://gitlab.com/pycqa/flake8/issues/19#note_712215

and Ian Cordasco said this looks like a bug in the unittest module, not py-flake8.