fix(tests): new test for utils module

tests/utils.rs

@@ -14,6 +14,13 @@ fn in_direction_end_oob() {
     assert_eq!(in_direction((0, 7), (-1, 1), (8, 8)).next(), None);
 }
 
+#[test]
+fn in_direction_invalid() {
+    assert_eq!(in_direction((0, 8), (-1, 1), (8, 8)).next(), None);
+    assert_eq!(in_direction((8, 0), (-1, 1), (8, 8)).next(), None);
+    assert_eq!(in_direction((0, 7), (0, 0), (8, 8)).next(), None);
+}
+
 #[test]
 fn in_direction_valid() {
     assert_eq!(move_in_direction((1, 1), (1, 3), (2, 4)), None);