Pass

Superbra jobbat!!!

However, I failed to compile you library. I judge this to be a case of "but it works on my machine".

error[E0277]: the type `[Vec<u8>]` cannot be indexed by `u8`
   --> src\lib.rs:375:16
    |
375 |             if self.board[possible_moves[_i as usize][0]][1] == _BLACK {
    |                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ slice indices are of type `usize` or ranges of `usize`
    |
    = help: the trait `SliceIndex<[Vec<u8>]>` is not implemented for `u8`
    = note: required because of the requirements on the impl of `Index<u8>` for `Vec<Vec<u8>>`

error[E0277]: the type `[Vec<u8>]` cannot be indexed by `u8`
   --> src\lib.rs:376:20
    |
376 |                 if self.board[possible_moves[_i as usize][1]][1] == _WHITE {
    |                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ slice indices are of type `usize` or ranges of `usize`
    |
    = help: the trait `SliceIndex<[Vec<u8>]>` is not implemented for `u8`
    = note: required because of the requirements on the impl of `Index<u8>` for `Vec<Vec<u8>>`

error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0277`.
error: could not compile `ogronman-chess`

Tips: It is more efficient to search for check from the perspective of the king, rather than that from the opponent's pieces.

Your approach of defining position as Vec<u8> is slow, as it utilises heap memory. The sized type [u8; 2] or (u8, u8) is much quicker.

Start by compiling the project and inspect src/lib.rs around lines 375-376, where the reported indexing errors occur. Confirm the indexing types and rerun the build; done means ogronman-chess compiles without the two E0277 errors. The issue also notes possible position-representation and check-search optimizations, which may require separate investigation.