Thanks for tackling this.  It's been bugging me almost daily this past week, but as usual when this bug is in my face I had no time to actually work on a fix.

I applied this patch to default,  put an invalid import in test_os, and this is the result:

rdmurray@pydev:~/python/p35>./python -m unittest test.test_os
Traceback (most recent call last):
  File "/home/rdmurray/python/p35/Lib/unittest/loader.py", line 140, in loadTestsFromName
    module = __import__(module_name)
  File "/home/rdmurray/python/p35/Lib/test/test_os.py", line 5, in <module>
    import foobar
ImportError: No module named 'foobar'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/rdmurray/python/p35/Lib/runpy.py", line 170, in _run_module_as_main
    "__main__", mod_spec)
  File "/home/rdmurray/python/p35/Lib/runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "/home/rdmurray/python/p35/Lib/unittest/__main__.py", line 18, in <module>
    main(module=None)
  File "/home/rdmurray/python/p35/Lib/unittest/main.py", line 92, in __init__
    self.parseArgs(argv)
  File "/home/rdmurray/python/p35/Lib/unittest/main.py", line 139, in parseArgs
    self.createTests()
  File "/home/rdmurray/python/p35/Lib/unittest/main.py", line 146, in createTests
    self.module)
  File "/home/rdmurray/python/p35/Lib/unittest/loader.py", line 202, in loadTestsFromNames
    suites = [self.loadTestsFromName(name, module) for name in names]
  File "/home/rdmurray/python/p35/Lib/unittest/loader.py", line 202, in <listcomp>
    suites = [self.loadTestsFromName(name, module) for name in names]
  File "/home/rdmurray/python/p35/Lib/unittest/loader.py", line 145, in loadTestsFromName
    next_attribute, self.suiteClass)
ValueError: need more than 1 value to unpack

I get similar errors if I misspell the module name in on the command line.

From my point of view this is still an improvement over the status quo, but I don't think it is what you had in mind :).