Suitable exceptions for setBoard with corresponding tests

app/src/main/java/sudoku/Solver.java

@@ -12,7 +12,11 @@ public class Solver implements SudokuSolver {
 
     /** {@inheritDoc} */
     @Override
-    public void setBoard(int[][] board) {
+    public void setBoard(int[][] board) throws IllegalArgumentException, NullPointerException {
+        if (board == null)
+            throw new NullPointerException("Board cannot be null");
+        if (board.length != 9 || board[0].length != 9)
+            throw new IllegalArgumentException("Board must be 9x9");
         this.board = board;
     }
 
@@ -107,7 +111,7 @@ public class Solver implements SudokuSolver {
         }
 
         // Recursively call randomizeBoard() until we get a solvable board
-        // This is expensive, and there should be some voodoo magic that computes this in n^2 time
+        // This is expensive, and there should be a better way to do this
         if (!isSolvable()) {
             randomizeBoard(difficulty);
         }

app/src/test/java/sudoku/SolverTest.java

@@ -106,4 +106,11 @@ class SolverTest {
         solver.set(7, 1, 8);
         assertFalse(solver.solve());
     }
+
+    @Test
+    void setBoardInvalidInputThrowsTest() {
+        Solver solver = new Solver();
+        assertThrows(NullPointerException.class, () -> solver.setBoard(null));
+        assertThrows(IllegalArgumentException.class, () -> solver.setBoard(new int[8][8]));
+    }
 }