Test: convert index

src/sudoku_solver.rs

@@ -13,7 +13,9 @@ impl SudokuSolver {
             playfield: playfield.clone(),
         }
     }
-    pub fn solve(&self) -> Playfield {
+    pub fn solve(&mut self) -> Playfield {
+        self.populate_possible_values();
+
         return self.playfield.clone();
     }