tox не работает при ImportError в python3.5

Это файл tox.ini:

[tox]
minversion = 2.4
envlist = py35, py36, py37, py38, pypy, pylint, benchmark
skip_missing_interpreters = true

[testenv:pylint]
deps =
   git+https://github.com/pycqa/astroid@master
   pytest
commands =
    # This would be greatly simplified by a solution for https://github.com/PyCQA/pylint/issues/352
    pylint -rn --rcfile={toxinidir}/pylintrc --load-plugins=pylint.extensions.docparams, pylint.extensions.mccabe \
    {toxinidir}/pylint \
    {toxinidir}/tests/message/ \
    {toxinidir}/tests/checkers/ \
    {toxinidir}/tests/extensions/ \
    {toxinidir}/tests/utils/ \
    {toxinidir}/tests/acceptance/ \
    {toxinidir}/tests/conftest.py \
    {toxinidir}/tests/test_config.py \
    {toxinidir}/tests/test_func.py \
    {toxinidir}/tests/test_functional.py \
    {toxinidir}/tests/test_import_graph.py \
    {toxinidir}/tests/test_pragma_parser.py \
    {toxinidir}/tests/test_pylint_runners.py \
    {toxinidir}/tests/test_regr.py \
    {toxinidir}/tests/test_self.py \
    {toxinidir}/tests/unittest_config.py \
    {toxinidir}/tests/lint/ \
    {toxinidir}/tests/unittest_pyreverse_diadefs.py \
    {toxinidir}/tests/unittest_pyreverse_inspector.py \
    {toxinidir}/tests/unittest_pyreverse_writer.py \
    {toxinidir}/tests/unittest_reporters_json.py \
    {toxinidir}/tests/unittest_reporting.py

[testenv:formatting]
basepython = python3
deps =
    black==20.8b1
    isort==5.5.2
commands =
    black --check . --exclude="tests/functional/|tests/input|tests/extensions/data|tests/regrtest_data/|tests/data/|venv|astroid|.tox"
    isort . --check-only
changedir = {toxinidir}

[testenv:mypy]
basepython = python3
deps =
    typed-ast>=1.4
    mypy>=0.7,<1.0

commands =
    python -m mypy {toxinidir}/pylint/checkers --ignore-missing-imports {posargs:}

[testenv]
deps =
   https://github.com/PyCQA/astroid/tarball/master#egg=astroid-master-2.0
   coverage<5.0
   mccabe
   # isort 5 is not compatible with Python 3.5
   py35: isort>=4.2.5,<5
   pytest
   pytest-xdist
   pytest-benchmark
   pytest-profiling

setenv =
    COVERAGE_FILE = {toxinidir}/.coverage.{envname}

commands =
    ; Run tests, ensuring all benchmark tests do not run
    python -Wignore -m coverage run -m pytest --benchmark-disable {toxinidir}/tests/ {posargs:}

    ; Transform absolute path to relative path
    ; for compatibility with coveralls.io and fix 'source not available' error.
    ; If you can find a cleaner way is welcome
    python -c "import os;cov_strip_abspath = open(os.environ['COVERAGE_FILE'], 'r').read().replace('.tox' + os.sep + os.path.relpath('{envsitepackagesdir}', '{toxworkdir}') + os.sep, '');open(os.environ['COVERAGE_FILE'], 'w').write(cov_strip_abspath)"
changedir = {toxworkdir}


[testenv:spelling]
deps =
   https://github.com/PyCQA/astroid/tarball/master#egg=astroid-master-2.0
   pytest
   pytest-xdist
   pyenchant

commands =
    python -Wi -m pytest {toxinidir}/tests/ {posargs:} -k unittest_spelling

changedir = {toxworkdir}

[testenv:coveralls]
setenv =
    COVERAGE_FILE = {toxinidir}/.coverage
passenv =
    *
deps =
    coverage<5.0
    coveralls
skip_install = true
commands =
    python -m coverage combine
    python -m coverage report --rcfile={toxinidir}/.coveragerc -m
    - coveralls --rcfile={toxinidir}/.coveragerc
changedir = {toxinidir}

[testenv:coverage-erase]
setenv =
    COVERAGE_FILE = {toxinidir}/.coverage
deps =
    coverage<5
skip_install = true
commands =
    python -m coverage erase
changedir = {toxinidir}

[testenv:coverage-html]
setenv =
    COVERAGE_FILE = {toxinidir}/.coverage
deps =
    coverage<5
skip_install = true
commands =
    python -m coverage combine
    python -m coverage html --ignore-errors --rcfile={toxinidir}/.coveragerc
changedir = {toxinidir}

[testenv:docs]
usedevelop = True
changedir = doc/
extras =
  docs
commands =
  sphinx-build -W -b html -d _build/doctrees . _build/html

[testenv:benchmark]
deps =
   https://github.com/PyCQA/astroid/tarball/master#egg=astroid-master-2.0
   coverage<5.0
   mccabe
   pytest
   pytest-xdist
   pygal
   pytest-benchmark

commands =
    ; Run the only the benchmark tests, grouping output and forcing .json output so we
    ; can compare benchmark runs
    python -Wi -m pytest --exitfirst \
                         --failed-first \
                         --benchmark-only \
                         --benchmark-save=batch_files \
                         --benchmark-save-data \
                         --benchmark-autosave \
                         {toxinidir}/tests \
                         --benchmark-group-by="group" \
                         {posargs:}

changedir = {toxworkdir}

А это conftest.py:

# pylint: disable=redefined-outer-name
# pylint: disable=no-name-in-module
import os

import pytest

from pylint import checkers
from pylint.lint import PyLinter
from pylint.testutils import MinimalTestReporter


@pytest.fixture
def linter(checker, register, enable, disable, reporter):
    _linter = PyLinter()
    _linter.set_reporter(reporter())
    checkers.initialize(_linter)
    if register:
        register(_linter)
    if checker:
        _linter.register_checker(checker(_linter))
    if disable:
        for msg in disable:
            _linter.disable(msg)
    if enable:
        for msg in enable:
            _linter.enable(msg)
    os.environ.pop("PYLINTRC", None)
    return _linter


@pytest.fixture(scope="module")
def checker():
    return None


@pytest.fixture(scope="module")
def register():
    return None


@pytest.fixture(scope="module")
def enable():
    return None


@pytest.fixture(scope="module")
def disable():
    return None


@pytest.fixture(scope="module")
def reporter():
    return MinimalTestReporter