Failed with just one test

"Single boolean" test
ReferenceError: cons is not defined
    at Context.<anonymous> (test.js:119:28)
    at process.processImmediate (node:internal/timers:471:21)

But don't know what "ReferenceError: cons is not defined" could mean under the hood, because in local

Set the log on input and output and output as expected for test:
My output: Token { text: 'true', type: 'boolean' }

Expected by the test:

 it('Single boolean', function() {
        var lexer = new Simplexer('true');
        assert.strictEqual(cons, true, 'Has next');
        assert.deepEqual(lexer.next(), new Token('true', 'boolean'));
    });

Actually

.Finally, the helper object ELEMENTS has been provided, which is a map from each element symbol to its corresponding full name (e.g. ELEMENTS['Na'] === 'Sodium').

I understand that is should be provided by me, despite of this is obvious... But now I understand that was provided by platform... A lot of time was required to build that list of elements actually...

Nice... in test implementation withSorting and nothing mentioned that in solution that is should be also...

Wich attempt generate different test scenarious...

This is random testing.

Just add elements which required during test

That is not correct, because tests passed and after pushing on "Sending" somewhere under the hood platform check something that is absent in the existing tests... And I have already spent 4 hours I am trying to figure out where to get these correct names and symbols..

It would be grat to have some of the link with all periodic table of elements.. In the internet in different places could same elements could be named differently (USA/Britain) and also in some places number of elements could be 118, in other 120...

In this task this tests is hidden and as a blackbox for developer, which list expected, because this is even missed in tests.

American chemical sosiety know just 118, but this task is not clear what exactly you are expecting here