TypeError: not all arguments converted during string formatting (on test test_e2e.py)

[marcosfromrio]

error: https://pastebin.com/uDgkjeaj
test file: https://pastebin.com/it1csGQW
dir tree: https://pastebin.com/tarfmUTE

(env) booktime_container $ pip list
Package Version

---

Django 2.1.5
Pillow 5.4.1
pip 18.1
psycopg2-binary 2.7.6.1
pytz 2018.9
selenium 3.141.0
setuptools 40.6.3
urllib3 1.24.1
wheel 0.32.3

~ $ geckodriver --version
geckodriver 0.23.0
The source code of this program is available from
testing/geckodriver in https://hg.mozilla.org/mozilla-central.
This program is subject to the terms of the Mozilla Public License 2.0.
You can obtain a copy of the license at https://mozilla.org/MPL/2.0/.

~ $ python3 --version
Python 3.7.2

~ $ firefox --version
Mozilla Firefox 64.0.2