How to resolve ‘Can’t perform this operation for unregistered loader type’

Problem

Recently I started to add unit tests using setuptools to one of my packages.

In order to do this, I added a test directory containing MyUnitTest.py. setup.py was properly setup using the

test_suite="tests"

option.

However, when running

python setup.py test

I got this error message:

running test
running egg_info
writing MyPackage.egg-info/PKG-INFO
writing top-level names to MyPackage.egg-info/top_level.txt
writing dependency_links to MyPackage.egg-info/dependency_links.txt
reading manifest file 'MyPackage.egg-info/SOURCES.txt'
reading manifest template 'MANIFEST.in'
writing manifest file 'MyPackage.egg-info/SOURCES.txt'
running build_ext
Traceback (most recent call last):
  File "setup.py", line 29, in <module>
    'Topic :: Scientific/Engineering :: Information Analysis'
  File "/usr/lib/python3.4/distutils/core.py", line 148, in setup
    dist.run_commands()
  File "/usr/lib/python3.4/distutils/dist.py", line 955, in run_commands
    self.run_command(cmd)
  File "/usr/lib/python3.4/distutils/dist.py", line 974, in run_command
    cmd_obj.run()
  File "/usr/lib/python3/dist-packages/setuptools/command/test.py", line 135, in run
    self.with_project_on_sys_path(self.run_tests)
  File "/usr/lib/python3/dist-packages/setuptools/command/test.py", line 116, in with_project_on_sys_path
    func()
  File "/usr/lib/python3/dist-packages/setuptools/command/test.py", line 160, in run_tests
    testLoader = cks
  File "/usr/lib/python3.4/unittest/main.py", line 92, in __init__
    self.parseArgs(argv)
  File "/usr/lib/python3.4/unittest/main.py", line 139, in parseArgs
    self.createTests()
  File "/usr/lib/python3.4/unittest/main.py", line 146, in createTests
    self.module)
  File "/usr/lib/python3.4/unittest/loader.py", line 146, in loadTestsFromNames
    suites = [self.loadTestsFromName(name, module) for name in names]
  File "/usr/lib/python3.4/unittest/loader.py", line 146, in <listcomp>
    suites = [self.loadTestsFromName(name, module) for name in names]
  File "/usr/lib/python3.4/unittest/loader.py", line 117, in loadTestsFromName
    return self.loadTestsFromModule(obj)
  File "/usr/lib/python3/dist-packages/setuptools/command/test.py", line 26, in loadTestsFromModule
    for file in resource_listdir(module.__name__, ''):
  File "/usr/lib/python3/dist-packages/pkg_resources.py", line 954, in resource_listdir
    resource_name
  File "/usr/lib/python3/dist-packages/pkg_resources.py", line 1378, in resource_listdir
    return self._listdir(self._fn(self.module_path,resource_name))
  File "/usr/lib/python3/dist-packages/pkg_resources.py", line 1415, in _listdir
    "Can't perform this operation for unregistered loader type"
NotImplementedError: Can't perform this operation for unregistered loader type

Solution

The issue is that your tests directory (and possibly any subdirectories) is not a Python module.

In order to fix this, add an __init__.py file to the tests directory (and possibly any subdirectories). In order to resolve the issue outlined above, it does not need any content

touch tests/__init__.py

After that, you should be able to run python setup.py test successfully.