Working parser, file chooser and sample files

app/src/test/java/sudoku/SudokuParserTest.java

@@ -0,0 +1,17 @@
+package sudoku;
+
+import org.junit.jupiter.api.Test;
+import static org.junit.jupiter.api.Assertions.*;
+
+public class SudokuParserTest {
+    @Test
+    void constructorTest() {
+        int[][] board;
+        try {
+            board = SudokuParser.parseSudoku("sample_sudokus/demo_from_lab.txt");
+        } catch (Exception e) {
+            board = null;
+        }
+        assertNotNull(board);
+    }
+}