implement SudokuSolver.validate() method and write unit tests for method

controllers/sudoku-solver.js

@@ -1,18 +1,27 @@
 class SudokuSolver {
 
     validate(puzzleString) {
+
+        return puzzleString.length == 81 && !puzzleString.match(/[^\.\d]/g);
+
     }
 
     checkRowPlacement(puzzleString, row, column, value) {
 
+
+
     }
 
     checkColPlacement(puzzleString, row, column, value) {
 
+
+
     }
 
     checkRegionPlacement(puzzleString, row, column, value) {
 
+        
+
     }
 
     solve(puzzleString) {