No, the kata test cases all provide a list with exactly one duplicated element, so both start and end will have actual numerical values; to be specific - index of the first occurence of the duplicated element and the index of the second occurence of the same element. These are then used to return the expected slice of the input list.

ok so you mean that the start variable automatically takes the value of the first variable which is related to the end counter?
So if no variables allow the counter to reach greater than 1 then the value of start would have been None, right?

in case of that kata, the right side of the first assignment will always return a list with two values (the input list will only have one duplicated element, so the condition arr.count(x) > 1 will be met only for two identical elements), thus the assignment start, end = [...] will assign a first value to start and second to end. The values are indices of this elements, beacuse as you can see I am using the enumerate function (for more info check the Python docs on enumerate) on the input array.

They are just declaring a variable they will use to store the index of the first repeated element

can someone tell me what does the start refer to ?

read the comments

I don't understand how it can be used to pass the test ?