An ember-cli test stub that's erroring

Testing
1

We haven’t written any of our own tests yet (so this is from ember-cli’s test stubs) but on running /tests in the browser, the following error occurs:

slug: it works (1, 0, 1)Rerun4 ms
failed, expected argument to be truthy, was: undefined

Ember slug test failing

In tests/unit/utils/slug-test.js there’s this:

import slug from '../../../utils/slug';

The file slug.js is in app/utils/ so the (literal) path is ‘…/…/…/app/utils/slug’

Here’s the code from /app/utils/slug:

export default function slug(str) {
  if (!str) { return; }
  str = str.replace(/^\s+|\s+$/g, ''); // trim
  str = str.toLowerCase();
  // remove accents, swap ñ for n, etc
  var from = "ãàáäâẽèéëêìíïîõòóöôùúüûñç·/_,:;";
  var to   = "aaaaaeeeeeiiiiooooouuuunc------";
  for (var i=0, l=from.length ; i<l ; i++) {
    str = str.replace(new RegExp(from.charAt(i), 'g'), to.charAt(i));
  }
  str = str.replace(/[^a-z0-9 -]/g, '') // remove invalid chars
    .replace(/\s+/g, '-') // collapse whitespace and replace by -
    .replace(/-+/g, '-'); // collapse dashes
  return str;
}

It’s unclear from the message which argument should be truthy?

I have this on SO too.