python setup.py test does not work yet

```
$ python setup.py test
running test
running egg_info
writing build_util.egg-info/PKG-INFO
writing dependency_links to build_util.egg-info/dependency_links.txt
writing requirements to build_util.egg-info/requires.txt
writing top-level names to build_util.egg-info/top_level.txt
reading manifest file 'build_util.egg-info/SOURCES.txt'
writing manifest file 'build_util.egg-info/SOURCES.txt'
running build_ext
tests (unittest.loader._FailedTest) ... ERROR

======================================================================
ERROR: tests (unittest.loader._FailedTest)
----------------------------------------------------------------------
ImportError: Failed to import test module: tests
Traceback (most recent call last):
File "~/anaconda3/lib/python3.7/unittest/loader.py", line 154, in loadTestsFromName
module = __import__(module_name)
ModuleNotFoundError: No module named 'build_util.tests'

----------------------------------------------------------------------
Ran 1 test in 0.000s

FAILED (errors=1)
Test failed:
error: Test failed:
```

Start by inspecting setup.py and the project’s tests package, then reproduce the failure with python setup.py test. Trace how the test command resolves the tests module and compare that with the package layout shown by the ImportError. Done means the command discovers the intended tests and completes without the reported import error.

Written by the indexing model from the issue text.