Thank you for the helpful advice. This will be very useful for me in the following exercises.

Or you can print the input yourself: https://docs.codewars.com/training/troubleshooting#print-input

My code passed "TEST" but failed "ATTEMPT". Some of the tests in "ATTEMPT" returned an error:

{'pos': [2, 5, 8], 'peaks': [20, 12, 20]} should equal {'pos': [2, 5, 8, 11], 'peaks': [20, 12, 20, 12]}

The problem is that in "ATTEMPT", the error messages do not contain the input data. Which makes it very difficult to understand what exactly is not working correctly in my code. Please improve the error message in "ATTEMPT". So that the student can see exactly which input data was passed to the code.

How is 7 a peak?

it is not, it is the index of a peak. in this kata, you have to return an array of peaks and an array of their indices

I don't know what values take WA for x-axis there, but they are wrong. Try with this other one: https://www.wolframalpha.com/input?i=plot+%5B%280%2C3%29%2C+%281%2C+2%29%2C+%282%2C+3%29%2C+%283%2C+6%29%2C+%284%2C+4%29%2C+%285%2C+1%29%2C+%286%2C+2%29%2C+%287%2C+3%29%2C+%288%2C+2%29%2C+%289%2C+1%29%2C+%2810%2C+2%29%2C+%2811%2C+3%29%5D&lang=es

I guess OP confusion came from the wrong graphic representation.

You're looking for all the peaks (think: mountain peaks), not just the highest one. The image you showed displays them both pretty well.

I'm a little bit confused:

[Example: pickPeaks([3, 2, 3, 6, 4, 1, 2, 3, 2, 1, 2, 3]) should return {pos: [3, 7], peaks: [6, 3]} (or equivalent in other languages)]

How is 7 a peak?

https://www.wolframalpha.com/input?i=plot+%5B3%2C+2%2C+3%2C+6%2C+4%2C+1%2C+2%2C+3%2C+2%2C+1%2C+2%2C+3%5D

That plateau after the peak is not a plateau-peak, it's just a plateau.

At index 20 there is a plateau-peak.

for arr [1,2,5,4,3,2,3,6,4,1,2,3,3,4,5,3,2,1,2,3,5,5,4,3],
expected { pos: [ 2, 7, 14 ], peaks: [ 5, 6, 5 ] } to deeply equal { pos: [ 2, 7, 14, 20 ], peaks: [ 5, 6, 5, 5 ] }. How ?

expected { pos: [ 2, 3 ], peaks: [ 3, 2 ] } to deeply equal { pos: [ 2 ], peaks: [ 3 ] }
assert.deepEqual(pickPeaks([2,1,3,2,2,2,2,5,6]), {pos:[2], peaks:[3]});

why?

{'pos': [3, 7], 'peak': [6, 3]} should equal 
{'pos': [3, 7], 'peaks': [6, 3]}
                     ^

They're not.

{'pos': [3, 7], 'peak': [6, 3]} should equal {'pos': [3, 7], 'peaks': [6, 3]}
{'pos': [3, 7], 'peak': [6, 3]} should equal {'pos': [3, 7], 'peaks': [6, 3]}
{'pos': [3, 7, 10], 'peak': [6, 3, 2]} should equal {'pos': [3, 7, 10], 'peaks': [6, 3, 2]}
TF is this? These are completely SAME (pls help)

Finding thepeaks is not difficult, but your wanted solution with a Map and List is confusing, why not use a Map and put a position and a peakheight together?

https://www.codewars.com/kata/5279f6fe5ab7f447890006a7/discuss#64f5b8c72b610bbbb906767f