What should contain the simplest custom tab?

Hi All,

I am just trying to get more familiar with implementing process on 6.0.0.2. I made quite simple tab and tried to implement it to front, but it gets stuck. The output looks like this:
Uncaught Error: No addons/tabs/customsimple-tab
callDep almond.js:180
req almond.js:349
makeRequire almond.js:155
_addAction sunstone.js:112
_addActions sunstone.js:124
each jQuery
_addActions sunstone.js:123
_addMainTabs sunstone.js:101
app.js:48
jQuery 3
app.js:46
main almond.js:318
callDep almond.js:176
main almond.js:309
req almond.js:392
setTimeout handler*req almond.js:391
main.js:263
almond.js:180
callDep almond.js:180
req almond.js:349
makeRequire almond.js:155
_addAction sunstone.js:112
_addActions sunstone.js:124
each jQuery
_addActions sunstone.js:123
_addMainTabs sunstone.js:101
<анонимный> app.js:48
jQuery 3
<анонимный> app.js:46
main almond.js:318
callDep almond.js:176
main almond.js:309
req almond.js:392
(Асинхронный: setTimeout handler)
req almond.js:391
<анонимный> main.js:263

Of course I have checked the addon-appmarket example, but it is quite complicative, what if I will need to implement something more simple?
So my question is: “what should contain the simplest tab, how looks minimal file structure for tab?”

Thanks in advance. All the best!