diff --git a/src/repr.rs b/src/repr.rs
index 4db7a30..476290e 100644
--- a/src/repr.rs
+++ b/src/repr.rs
@@ -79,6 +79,7 @@ impl Board {
             return;
         };
 
+        // Create all chains from the piece being propegated from in `i` and `j` coordinates
         let mut chains: Vec<Vec<(usize, usize)>> = split_from(0, BOARD_SIZE - 1, i)
             .into_iter()
             .map(|range| range.into_iter().map(|i| (i, j)).collect())
@@ -87,7 +88,7 @@ impl Board {
             &mut split_from(0, BOARD_SIZE - 1, j)
                 .into_iter()
                 .map(|range| range.into_iter().map(|j| (i, j)).collect())
-                .collect::<Vec<Vec<(usize, usize)>>>(),
+                .collect(),
         );
 
         for chain in chains {
@@ -100,15 +101,17 @@ impl Board {
                 if piece == &starting_color {
                     if chain_length > 0 {
                         // fill all opposite colors with this color
-                        let Some(i_o_s) = chain.get(..chain_length) else {
+                        let Some(history) = chain.get(..chain_length) else {
                             break;
                         };
 
                         // fill all opposite colors with this color
-                        for &(i_o, j_o) in i_o_s {
+                        for &(i_o, j_o) in history {
                             self.place_and_prop_unchecked(i_o, j_o, starting_color);
                         }
                     }
+                    // either the other pieces were replaced, or this was an invalid chain,
+                    // in both cases, the loop needs to be breaked
                     break;
                 }
                 chain_length += 1;
@@ -138,8 +141,6 @@ impl Board {
 mod test {
     use super::*;
 
-    // TODO! add tests for double prop
-
     #[test]
     fn place_and_get() {
         let mut board = Board::new();
@@ -235,4 +236,46 @@ mod test {
             );
         }
     }
+
+    #[test]
+    fn double_prop() {
+        let mut board = Board::new();
+        assert_eq!(board.place(0, 0, Piece::Black), Ok(()));
+
+        assert_eq!(board.place(0, 1, Piece::White), Ok(()));
+
+        // -----------------
+        // |□|■| | | | | | |
+        // -----------------
+        // | | | | | | | | |
+
+        assert_eq!(board.place(1, 1, Piece::White), Ok(()));
+
+        // -----------------
+        // |□|■| | | | | | |
+        // -----------------
+        // | |■| | | | | | |
+
+        assert_eq!(board.place(2, 1, Piece::Black), Ok(()));
+
+        // -----------------
+        // |□|■| | | | | | |
+        // -----------------
+        // | |■| | | | | | |
+        // -----------------
+        // | |□| | | | | | |
+
+        assert_eq!(board.place(0, 2, Piece::Black), Ok(()));
+
+        // -----------------
+        // |□|□|□| | | | | |
+        // -----------------
+        // | |□| | | | | | |
+        // -----------------
+        // | |□| | | | | | |
+
+        assert_eq!(board.get(0, 1), &Some(Piece::Black));
+
+        assert_eq!(board.get(1, 1), &Some(Piece::Black));
+    }
 }