[board, position] Implement some methods to check for whether a king is in check

Remove some dead code from Position.

board/src/check.rs

@@ -0,0 +1,49 @@
+// Eryn Wells <eryn@erynwells.me>
+
+use crate::Board;
+use chessfriend_bitboard::BitBoard;
+use chessfriend_core::{Color, Piece};
+
+impl Board {
+    #[must_use]
+    pub fn active_color_is_in_check(&self) -> bool {
+        self.color_is_in_check(self.active_color)
+    }
+
+    #[must_use]
+    pub fn color_is_in_check(&self, color: Color) -> bool {
+        let king = self.king_bitboard(color);
+        let opposing_sight = self.opposing_sight(color);
+        (king & opposing_sight).is_populated()
+    }
+
+    fn king_bitboard(&self, color: Color) -> BitBoard {
+        self.pieces.find_pieces(Piece::king(color))
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::test_board;
+    use chessfriend_core::Color;
+
+    #[test]
+    fn active_color_is_in_check() {
+        let board = test_board!(
+            White King on A3,
+            Black Rook on F3,
+        );
+
+        assert!(board.color_is_in_check(Color::White));
+    }
+
+    #[test]
+    fn active_color_is_not_in_check() {
+        let board = test_board!(
+            White King on A3,
+            Black Rook on B4,
+        );
+
+        assert!(!board.color_is_in_check(Color::White));
+    }
+}

board/src/lib.rs

@@ -9,6 +9,7 @@ pub mod macros;
 pub mod movement;
 pub mod sight;
 
+mod check;
 mod piece_sets;
 
 pub use board::Board;