Question about optimize in Week 1 Programming Assignment 2

In the second programming assignment Exercise 3, X and Y are inputs with the following description:

X -- list of integers, where each integer is a number that maps to a character in the vocabulary.
Y -- list of integers, exactly the same as X but shifted one index to the left.

Does the description mean that Y[i] = X[i+1], X[0] = 0, and Y[-1] = 0 (indicating ‘\n’) to line up with the expected input/output for one example for this language model? I’m confused as in optimize_test this is not the case:

X = [12, 3, 5, 11, 22, 3]
Y = [4, 14, 11, 22, 25, 26]

A test can can contain any data desired - it does not have to represent a real situation.
The purpose of a test case is to explore whether your code gives the expected outputs for a given set of data.

Maybe it would be more logical if the X and Y values matched the expectations, but it isn’t strictly required.