`python setup.py test` crashes if `test_suite` is not set and `use_2to3` is True

[anntzer]

With the following setup.py:

from setuptools import setup

setup(
    name='foo',
    py_modules=['foo'],
    use_2to3=True,
)

and an empty foo.py, python3 setup.py test crashes with:

running test
running build_py
running egg_info
writing /tmp/foo/build/lib/foo.egg-info/PKG-INFO
writing dependency_links to /tmp/foo/build/lib/foo.egg-info/dependency_links.txt
writing top-level names to /tmp/foo/build/lib/foo.egg-info/top_level.txt
reading manifest file '/tmp/foo/build/lib/foo.egg-info/SOURCES.txt'
writing manifest file '/tmp/foo/build/lib/foo.egg-info/SOURCES.txt'
running build_ext
TS None True
Traceback (most recent call last):
  File "setup.py", line 6, in <module>
    use_2to3=True,
  File "/usr/lib/python3.5/distutils/core.py", line 148, in setup
    dist.run_commands()
  File "/usr/lib/python3.5/distutils/dist.py", line 955, in run_commands
    self.run_command(cmd)
  File "/usr/lib/python3.5/distutils/dist.py", line 974, in run_command
    cmd_obj.run()
  File "/usr/lib/python3.5/site-packages/setuptools/command/test.py", line 170, in run
    self.run_tests()
  File "/usr/lib/python3.5/site-packages/setuptools/command/test.py", line 178, in run_tests
    module = self.test_suite.split('.')[0]
AttributeError: 'NoneType' object has no attribute 'split'

[jaraco]

use_2to3 has been removed in v58.