refactor isValid

app/src/main/java/sudoku/structure/MultiDoku.java

@@ -112,11 +112,11 @@ public class MultiDoku {
 	 * @return boolean, true s'il est valide et false sinon.
 	 */
 	public boolean isValid() {
-		boolean result = true;
 		for (Sudoku sudoku : this.subGrids) {
-			result = sudoku.isValid() && result;
+			if(!sudoku.isValid())
+				return false;
 		}
-		return result;
+		return true;
 	}
 
 	@Override

app/src/test/java/sudoku/SudokuSerializerTest.java

@@ -1,5 +1,6 @@
 package sudoku;
 
+import java.io.File;
 import java.util.Random;
 
 import org.json.JSONObject;
@@ -25,6 +26,9 @@ public class SudokuSerializerTest {
         try {
             otherDoku = SudokuFactory.fromfile(savePath);
             assert (otherDoku != null);
+            // clean file after test
+            File fileToDelete = new File(savePath);
+            fileToDelete.delete();
         } catch (Exception e) {
             e.printStackTrace();
             assert false;