"unable to open X server"

I’m working on setting up testing for the first time, but the CircleCI app is showing this weird error on the “Test” step:

#!/bin/bash -eo pipefail sh ./tests/manage.py test

import-im6.q16: unable to open X server `' @ error/import.c/ImportImageCommand/360. ./tests/manage.py: 2: ./tests/manage.py: Syntax error: word unexpected (expecting ")") Exited with code exit status 2

CircleCI received exit code 2

I can’t find any other references on Google to that error in the context of CircleCI, so I’m assuming that I did something horribly wrong.

Here’s the (WIP) repository: GitHub - Pikamander2/helperfunctions: Miscellaneous Python helper functions

What would cause that error? I’m just looking to set up simple automated testing, nothing fancy.