oooooh. know I get it. You should add this example to the instructions for people like me :)

And another problem. Input:

arrayOfArrays: [[71, 39, 28, -91, -6], [-77, 24, 29, 51, -90], [-78, -81, 10, -13, -54], [55, -17, 7, -45, 58]] 
shift: 2

So algorithm is something like:

[71, 39, 28, -91, -6]
            [-77, 24, 29, 51, -90]
                        [-78, -81, 10, -13, -54]
                                       [55, -17, 7, -45, 58]

And the result is: [71, 39, 28, -168, 18, 29, -27, -171, 10, 42, -71, 7, -45, 58], but test expects: [71, 39, -49, -67, -55, -30, -25, -30, -47, -45, 58]
I can be mistaken, but I guess with shift = 2 and arrays size = 5, the first 3 elements of the first array must be in the result. So the result array must start with [71, 39, 28...], when test expexts [71, 39, -49...]. Why?

Now everything is correct with sizes! Thanks!

In the Ruby version something is wrong with tests. Or I missunderstood something. The instructions says: "The arrays in the array will all have the same size and this size will always be greater than 0.", but i get arrays with different size. Example input:

arrayOfArrays: [[7, 73, -58, 1, 49, -10, -55, 16, -78], [-48, -69, 40, 99, -88, 73], [-34, -79, 70, 98, 25, 100, 12, 38, 17, 2]]
shift: 1