Just print the Dictionary to the Console and click on the Test button:

E.g in C#:

foreach(var el in ELEMENTS)
  Console.WriteLine(el);

You seem to have outdated sample tests. You can either:

• Reset the trainer (removes your code, so save it)
• Ignore the sample tests and just hit "attempt"

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

I'm pretty sure you missed this line from the description:

...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').

somewhere under the hood platform check something that is absent in the existing tests...

Because the tests expect you to handle it using the given ELEMENTS object. And of course, in sample tests the author can't add all elements as examples. That's why you can't make your own object based on what is shown in the sample tests.

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..

This kata does not require you to actually know the periodic table and all its elements. They are provided for you. You can solve this without knowing a single element's name, theoretically.

Any nitpicks about scientific accuracy would pass by 99.9% of this platform's audience.

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