I forgor that one case

src/rules/game_tile.rs

@@ -101,7 +101,9 @@ impl Tile {
             if on_board {
                 //If a future rock position is not empty then the move is not valid.
                 if size == 2 && state[rock_y as usize][rock_x as usize] != Tile::Empty {
-                    return false;
+                    if state[new_y as usize][new_x as usize] != Tile::Empty || state[step_y as usize][step_x as usize] != Tile::Empty {
+                        return false;
+                    }
                 }
             }
 

src/rules/tests.rs

@@ -1184,4 +1184,30 @@ fn squish_test_3(){
     //Not supposed to do that.
     assert!(!Tile::is_valid(&board, (2, 2), (0, 0), true));
     assert!(!Tile::aggressive_move(&mut board, (2, 2), (0, 0)));
+}
+
+
+#[test]
+fn squish_test_4(){
+    let state: [[Tile; 4]; 4] = [
+        [Tile::Empty, Tile::Empty, Tile::Empty, Tile::Black],
+        [Tile::Empty, Tile::Empty, Tile::Empty, Tile::Empty],
+        [Tile::Empty, Tile::Empty, Tile::Empty, Tile::Empty],
+        [Tile::White, Tile::Empty, Tile::Empty, Tile::Empty],
+    ];
+
+    let target_state: [[Tile; 4]; 4] = [
+        [Tile::Empty, Tile::Empty, Tile::Empty, Tile::Black],
+        [Tile::Empty, Tile::Empty, Tile::White, Tile::Empty],
+        [Tile::Empty, Tile::Empty, Tile::Empty, Tile::Empty],
+        [Tile::Empty, Tile::Empty, Tile::Empty, Tile::Empty],
+    ];
+
+    let mut board = Board::new_board(Tile::Black, Tile::Black);
+    board.set_state(&state);
+
+    //Not supposed to do that.
+    assert!(Tile::is_valid(&board, (3, 0), (1, 2), true));
+    assert!(Tile::aggressive_move(&mut board, (3, 0), (1, 2)));
+    assert_eq!(*board.get_state(), target_state);
 }