Error when running 'bench run-ui-tests'

I’ve made some css changes to make desk full-width, and I’m preparing to make a pull request. However, for some reason I keep getting this error when I run bench run-ui-tests --app frappe:

Johns-MacBook-Pro:contrib-bench John$ bench run-ui-tests --app frappe
Running frappe/tests/ui/test_number_format.js...
ERROR: test_test_runner (frappe.tests.ui.test_test_runner.TestTestRunner)
Traceback (most recent call last):
  File "/Users/John/Dev/benches/contrib- 
bench/apps/frappe/frappe/tests/ui/", line 40, in test_test_runner
    console = driver.get_console()
  File "/Users/John/Dev/benches/contrib-bench/apps/frappe/frappe/utils/", line 153, in get_console
    message = literal_eval(message)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/", line 49, in literal_eval
    node_or_string = parse(node_or_string, mode='eval')
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/", line 37, in parse
    return compile(source, filename, mode, PyCF_ONLY_AST)
  File "<unknown>", line 1
    "quill" "Overwriting modules/mention with" class Mention {
SyntaxError: invalid syntax

Ran 1 test in 18.916s

FAILED (errors=1)

Has anyone else run these tests successfully, or gotten this error before? Maybe it has something to do with passing javascript to literal_eval?