pytest tests error

[sanitaminimalist]

When I run command "pytest tests", I get this errors:

Traceback (most recent call last):
File "/usr/local/lib/python3.5/site-packages/_pytest/config.py", line 329, in _getconftestmodules
return self._path2confmods[path]
KeyError: local('/root/casper/tests')

During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "/usr/local/lib/python3.5/site-packages/_pytest/config.py", line 360, in _importconftest
return self._conftestpath2mod[conftestpath]
KeyError: local('/root/casper/tests/conftest.py')

During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "/usr/local/lib/python3.5/site-packages/_pytest/config.py", line 366, in _importconftest
mod = conftestpath.pyimport()
File "/usr/local/lib/python3.5/site-packages/py/_path/local.py", line 668, in pyimport
import(modname)
File "/usr/local/lib/python3.5/site-packages/pytest/assertion/rewrite.py", line 213, in load_module
py.builtin.exec(co, mod.dict)
File "/root/casper/tests/conftest.py", line 3, in
import rlp
File "/usr/local/lib/python3.5/site-packages/rlp/init.py", line 1, in
from . import sedes # noqa: F401
File "/usr/local/lib/python3.5/site-packages/rlp/sedes/init.py", line 4, in
from .big_endian_int import BigEndianInt, big_endian_int # noqa: F401
File "/usr/local/lib/python3.5/site-packages/rlp/sedes/big_endian_int.py", line 1, in
from eth_utils import (
File "/usr/local/lib/python3.5/site-packages/eth_utils/init.py", line 24, in
from .applicators import ( # noqa: F401
File "/usr/local/lib/python3.5/site-packages/eth_utils/applicators.py", line 3, in
from cytoolz.functoolz import (
File "/usr/local/lib/python3.5/site-packages/cytoolz/init.py", line 3, in
from .functoolz import *
ImportError: /usr/local/lib/python3.5/site-packages/cytoolz/functoolz.cpython-35m-x86_64-linux-gnu.so: undefined symbol: PyFPE_jbuf
ERROR: could not load /root/casper/tests/conftest.py