Why doesn't tox run pytests?

I have the following tox.ini:

[tox]
envlist = py35
deps =
    pytest
    pytest-cov
    pytest-pep8
commands = py.test

and the following setup.cfg:

[metadata]
description-file = README.md

[tool:pytest]
addopts = ./tests/ --doctest-modules --cov=./lidtk --cov-report html:tests/reports/coverage-html --pep8
doctest_encoding = utf-8

When I run py.test, I get 1 failling test (intentionally, I changed one test so that it fails). But when I run tox in the folder, I get:

GLOB sdist-make: /home/moose/GitHub/lidtk/setup.py
py35 inst-nodeps: /home/moose/GitHub/lidtk/.tox/dist/lidtk-0.1.0.zip
WARNING:Discarding $PYTHONPATH from environment, to override specify PYTHONPATH in 'passenv' in your configuration.
py35 installed: beautifulsoup4==4.6.0,certifi==2017.11.5,cffi==1.11.3,chardet==3.0.4,cld2-cffi==0.1.4,idna==2.6,lidtk==0.1.0,pycparser==2.18,PyYAML==3.12,requests==2.18.4,six==1.11.0,urllib3==1.22,wikipedia==1.4.0
py35 runtests: PYTHONHASHSEED='465380300'
________________________________________________________________________________ summary ________________________________________________________________________________
  py35: commands succeeded
  congratulations :)

Why doesn't tox run py.test?

In case there are more questions: All of the code is on GitHub.