Test unit.common.test_utils.test_latin_str_to_unicode failed if you try run in with covearge

If you run tests with coverage, test fuelclient.tests.unit.common.test_utils.TestUtils.test_latin_str_to_unicode fail
FAIL: fuelclient.tests.unit.common.test_utils.TestUtils.test_latin_str_to_unicode
tags: worker-0
----------------------------------------------------------------------
Empty attachments:
  pythonlogging:''
  stderr
  stdout

Traceback (most recent call last):
  File "/home/romcheg/projects/python-fuelclient/.tox/cover/local/lib/python2.7/site-packages/mock/mock.py", line 1305, in patched
    return func(*args, **keywargs)
  File "fuelclient/tests/unit/common/test_utils.py", line 240, in test_latin_str_to_unicode
    test_data = 'czegoś' if six.PY3 else u'czegoś'.encode('iso-8859-16')
  File "/home/romcheg/projects/python-fuelclient/.tox/cover/lib/python2.7/encodings/__init__.py", line 100, in search_function
    level=0)
  File "/home/romcheg/projects/python-fuelclient/.tox/cover/local/lib/python2.7/site-packages/coverage/control.py", line 587, in _should_trace
    disp = self._should_trace_internal(filename, frame)
  File "/home/romcheg/projects/python-fuelclient/.tox/cover/local/lib/python2.7/site-packages/coverage/control.py", line 489, in _should_trace_internal
    canonical = files.canonical_filename(filename)
  File "/home/romcheg/projects/python-fuelclient/.tox/cover/local/lib/python2.7/site-packages/coverage/files.py", line 69, in canonical_filename
    cf = abs_file(filename)
  File "/home/romcheg/projects/python-fuelclient/.tox/cover/local/lib/python2.7/site-packages/coverage/files.py", line 152, in abs_file
    path = unicode_filename(path)
  File "/home/romcheg/projects/python-fuelclient/.tox/cover/local/lib/python2.7/site-packages/coverage/files.py", line 137, in unicode_filename
    filename = filename.decode(encoding, "replace")
LookupError: unknown encoding: iso-8859-16
Ran 327 tests in 4.665s (+0.031s)
FAILED (id=26, failures=1)
error: testr failed (1)
ERROR: InvocationError: '/bin/bash -c TESTS_DIR=./fuelclient/tests/unit python setup.py testr --coverage'