diff --git a/src/connect4/board.rs b/src/connect4/board.rs
index 9a41333..572fa87 100644
--- a/src/connect4/board.rs
+++ b/src/connect4/board.rs
@@ -4,10 +4,14 @@ use crate::{Player, State};
 
 type Position = Option<Player>;
 
-const BOARD_WIDTH: usize = 7;
-const BOARD_HEIGHT: usize = 4;
-const BOARD_POSITIONS: usize = BOARD_WIDTH * BOARD_HEIGHT;
+const WIDTH: usize = 7;
+const HEIGTH: usize = 4;
+const BOARD_POSITIONS: usize = WIDTH * HEIGTH;
 
+///  0  1  2  3  4  5  6
+///  7  8  9 10 11 12 13
+/// 14 15 16 17 18 19 20
+/// 21 22 23 24 25 26 27
 pub struct Board {
     positions: [Position; BOARD_POSITIONS],
 }
@@ -20,7 +24,14 @@ impl Board {
     }
 
     pub fn result(&self) -> State {
-        self.check_board()
+        match self.check_board() {
+            State::Winner(winner) => State::Winner(winner),
+            State::InProgress if self.positions.iter().all(|position| position.is_some()) => {
+                State::Draw
+            }
+            State::InProgress => State::InProgress,
+            State::Draw => unreachable!("check_board cannot tell a draw"),
+        }
     }
 
     fn check_board(&self) -> State {
@@ -30,15 +41,15 @@ impl Board {
     }
 
     fn check_columns(&self) -> State {
-        for i in 0..BOARD_WIDTH {
-            self.check_four(i, i + BOARD_WIDTH, i + 2 * BOARD_WIDTH, i + 3 * BOARD_WIDTH)?;
+        for i in 0..WIDTH {
+            self.check_four(i, i + WIDTH, i + 2 * WIDTH, i + 3 * WIDTH)?;
         }
 
         State::InProgress
     }
 
     fn check_rows(&self) -> State {
-        for row_start in 0..BOARD_HEIGHT {
+        for row_start in 0..HEIGTH {
             for offset in 0..4 {
                 let start = row_start + offset;
                 self.check_four(start, start + 1, start + 2, start + 3)?;
@@ -49,6 +60,17 @@ impl Board {
     }
 
     fn check_diagonals(&self) -> State {
+        // */*
+        for start in 3..WIDTH {
+            const DIFF: usize = WIDTH - 1;
+            self.check_four(start, start + DIFF, start + 2 * DIFF, start + 3 * DIFF)?;
+        }
+
+        // *\*
+        for start in 0..4 {
+            const DIFF: usize = WIDTH + 1;
+            self.check_four(start, start + DIFF, start + 2 * DIFF, start + 3 * DIFF)?;
+        }
         State::InProgress
     }
 
@@ -73,3 +95,74 @@ impl Index<usize> for Board {
         &self.positions[index]
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use crate::{Player, State};
+
+    use super::Board;
+
+    fn parse_board(board: &str) -> Board {
+        let positions = board
+            .chars()
+            .filter(|char| !char.is_whitespace())
+            .map(|char| match char {
+                'X' => Some(Player::X),
+                'O' => Some(Player::O),
+                '_' => None,
+                char => panic!("Invalid char in board: `{char}`"),
+            })
+            .collect::<Vec<_>>()
+            .try_into()
+            .expect(&format!(
+                "not enough positions provided: {}",
+                board.chars().filter(|c| !c.is_whitespace()).count()
+            ));
+
+        Board { positions }
+    }
+
+    fn test(board: &str, state: State) {
+        let board = parse_board(board);
+        assert_eq!(board.result(), state);
+    }
+
+    #[test]
+    fn draw() {
+        test(
+            "
+        XOOOXOX
+        XOOOXOX
+        OXXXOXO
+        XOOOXXX
+        ",
+            State::Draw,
+        );
+    }
+
+    #[test]
+    fn full_winner() {
+        test(
+            "
+        XOOOXOX
+        XOOOXOX
+        OXXXOXO
+        XOOOXOX
+        ",
+            State::Winner(Player::O),
+        );
+    }
+
+    #[test]
+    fn three_rows() {
+        test(
+            "
+        XXX_OOO
+        _XXX___
+        X_OOO__
+        OOO____
+        ",
+            State::InProgress,
+        );
+    }
+}