[position] Fix all the unit tests

The pawn move generator only generated pushes for white pawns.
The is_king_in_check returned an inverted flag.
MoveSet needed a couple more validation methods: can_move_to_square and can_castle.
The MakeMoveBuilder also needed a little more move validation using the above methods.

position/src/move_generator/move_set.rs

@@ -2,15 +2,16 @@
 
 use crate::{r#move::Castle, Move, MoveBuilder};
 use chessfriend_bitboard::BitBoard;
-use chessfriend_core::{Color, Piece, PlacedPiece, Shape};
+use chessfriend_core::{Color, Piece, PlacedPiece, Shape, Square};
 
+/// A set of bitboards defining the moves for a single piece on the board.
 #[derive(Clone, Debug, Default, Eq, PartialEq)]
 struct BitBoardSet {
     quiet: BitBoard,
     captures: BitBoard,
 }
 
-/// A set of moves for a piece on the board.
+/// A set of moves for a single piece on the board.
 #[derive(Clone, Debug, Eq, PartialEq)]
 pub(crate) struct MoveSet {
     piece: PlacedPiece,
@@ -27,6 +28,17 @@ impl MoveSet {
         }
     }
 
+    pub(crate) fn can_move_to_square(&self, to: Square) -> bool {
+        self.bitboard().is_set(to)
+    }
+
+    pub(crate) fn can_castle(&self, castle: Castle) -> bool {
+        match castle {
+            Castle::KingSide => (self.special & 0b1) != 0,
+            Castle::QueenSide => (self.special & 0b10) != 0,
+        }
+    }
+
     pub(super) fn quiet_moves(mut self, bitboard: BitBoard) -> MoveSet {
         self.bitboards.quiet = bitboard;
         self
@@ -52,7 +64,7 @@ impl MoveSet {
         self.bitboards.captures | self.bitboards.quiet
     }
 
-    pub(super) fn moves(&self) -> impl Iterator<Item = Move> + '_ {
+    pub(crate) fn moves(&self) -> impl Iterator<Item = Move> + '_ {
         let piece = self.piece.piece();
         let from_square = self.piece.square();
 

position/src/move_generator/pawn.rs

@@ -3,7 +3,7 @@
 use super::{move_generator_declaration, MoveGeneratorInternal, MoveSet};
 use crate::Position;
 use chessfriend_bitboard::BitBoard;
-use chessfriend_core::{Piece, PlacedPiece, Rank, Shape, Square};
+use chessfriend_core::{Color, PlacedPiece, Rank, Shape, Square};
 
 #[derive(Debug)]
 struct MoveIterator(usize, usize);
@@ -32,18 +32,31 @@ impl MoveGeneratorInternal for PawnMoveGenerator {
 
 impl PawnMoveGenerator {
     fn pushes(position: &Position, piece: PlacedPiece) -> BitBoard {
+        let color = piece.color();
         let square = piece.square();
         let bitboard: BitBoard = square.into();
 
-        let starting_rank = Rank::PAWN_STARTING_RANKS[piece.color() as usize];
-
+        let starting_rank = Rank::PAWN_STARTING_RANKS[color as usize];
         let empty_squares = position.empty_squares();
-        let mut moves = bitboard.shift_north_one() & empty_squares;
-        if !(bitboard & BitBoard::rank(starting_rank.as_index())).is_empty() {
-            moves |= moves.shift_north_one() & empty_squares;
-        }
 
-        moves
+        match color {
+            Color::White => {
+                let mut moves = bitboard.shift_north_one() & empty_squares;
+                if !(bitboard & BitBoard::rank(starting_rank.as_index())).is_empty() {
+                    moves |= moves.shift_north_one() & empty_squares;
+                }
+
+                moves
+            }
+            Color::Black => {
+                let mut moves = bitboard.shift_south_one() & empty_squares;
+                if !(bitboard & BitBoard::rank(starting_rank.as_index())).is_empty() {
+                    moves |= moves.shift_south_one() & empty_squares;
+                }
+
+                moves
+            }
+        }
     }
 
     fn attacks(position: &Position, piece: PlacedPiece) -> BitBoard {
@@ -63,7 +76,7 @@ impl PawnMoveGenerator {
 mod tests {
     use super::*;
     use crate::{assert_move_list, position::DiagramFormatter, test_position, Move, MoveBuilder};
-    use chessfriend_core::{piece, Color, Square};
+    use chessfriend_core::{piece, Color, Piece, Square};
     use std::collections::HashSet;
 
     #[test]