cleanup test + ensure chain validity

src/board.rs

@@ -53,6 +53,15 @@ fn gen_adj_lookup() -> PosMap<ChainCollection> {
 
                     // handle diagonals
                     chains.extend(diag_raw(i_chain, j_chain).map(Iterator::collect));
+
+                    // make sure all chains are in the proper range so we can ignore bounds checking later
+                    assert!(
+                        chains.iter().all(|x| x.iter().all(
+                            |(i, j)| (0..BOARD_SIZE).contains(i) && (0..BOARD_SIZE).contains(j)
+                        )),
+                        "chains go out-of-bounds"
+                    );
+
                     chains
                 })
                 .collect()