I just got the following traceback when trying discover without 3.5. It runs fine under 3.4...

$ ~/cpython/default/python -m unittest discover -v
Traceback (most recent call last):
  File "/home/antoine/cpython/default/Lib/runpy.py", line 170, in _run_module_as_main
    "__main__", mod_spec)
  File "/home/antoine/cpython/default/Lib/runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "/home/antoine/cpython/default/Lib/unittest/__main__.py", line 18, in <module>
    main(module=None)
  File "/home/antoine/cpython/default/Lib/unittest/main.py", line 93, in __init__
    self.runTests()
  File "/home/antoine/cpython/default/Lib/unittest/main.py", line 244, in runTests
    self.result = testRunner.run(self.test)
  File "/home/antoine/cpython/default/Lib/unittest/runner.py", line 168, in run
    test(result)
  File "/home/antoine/cpython/default/Lib/unittest/suite.py", line 87, in __call__
    return self.run(*args, **kwds)
  File "/home/antoine/cpython/default/Lib/unittest/suite.py", line 125, in run
    test(result)
  File "/home/antoine/cpython/default/Lib/unittest/suite.py", line 87, in __call__
    return self.run(*args, **kwds)
  File "/home/antoine/cpython/default/Lib/unittest/suite.py", line 125, in run
    test(result)
  File "/home/antoine/cpython/default/Lib/unittest/suite.py", line 87, in __call__
    return self.run(*args, **kwds)
  File "/home/antoine/cpython/default/Lib/unittest/suite.py", line 125, in run
    test(result)
  File "/home/antoine/cpython/default/Lib/unittest/case.py", line 625, in __call__
    return self.run(*args, **kwds)
  File "/home/antoine/cpython/default/Lib/unittest/case.py", line 553, in run
    result.startTest(self)
  File "/home/antoine/cpython/default/Lib/unittest/runner.py", line 54, in startTest
    self.stream.write(self.getDescription(test))
  File "/home/antoine/cpython/default/Lib/unittest/runner.py", line 47, in getDescription
    return '\n'.join((str(test), doc_first_line))
  File "/home/antoine/cpython/default/Lib/unittest/case.py", line 1354, in __str__
    self._testFunc.__name__)
AttributeError: 'str' object has no attribute '__name__'