What you see is a confusing message coming from Node8 tests. Please change to other version (preferrably the latest one, Node 18), and see that the reason of failing tests is different:

TypeError: Cannot read properties of null (reading 'length')
    at countSmileys (test.js:5:38)
    at doTest (test.js:17:24)
    at Context.<anonymous> (test.js:34:7)
    at process.processImmediate (node:internal/timers:471:21)

Your solution has a bug which you need to fix. I will try to take care of confusing messages.

You have a trailing whitespace. To see it, select Node v8. As it is an error in your code, I'll close this issue and I'll open a new one with the proper problem.