Ah, yeah, you don’t want to use find() when dealing with :contains, you will want to use exists()
Example of it at
https://github.com/discourse/discourse/blob/master/test/javascripts/acceptance/search-full-test.js.es6#L274-L287
IIRC, that is because find() will still return an empty object back and should be used with assert.equal so you can compare a specific attribute of what you expected to find to an expectation.
exists will handle that object being empty and treat it as “not found” or “false”
https://github.com/discourse/discourse/blob/master/test/javascripts/helpers/assertions.js#L3-L5