Modify and test bytes length serialization / deserialization for data…

… export/import #170 #269

lib/utils/export.dart

@@ -2,10 +2,11 @@ import 'dart:typed_data';
 
 List<int> lengthToBytes(int len) {
   final List<int> bytes = [];
-  bytes.add(len & 0xFF);
-  bytes.add(len & 0xFF00);
-  bytes.add(len & 0xFF0000);
-  bytes.add(len & 0xFF000000);
+  for (int i = 0; i < 4; i++) {
+    bytes.add(len & 0xFF);
+    len = len ~/ 256;
+  }
+
   return bytes;
 }
 

test/export_utils_test.dart

@@ -0,0 +1,21 @@
+import 'dart:math';
+
+import 'package:flutter_test/flutter_test.dart';
+import 'package:track_my_indoor_exercise/utils/export.dart';
+import 'utils.dart';
+
+main() {
+  group('int32 serialization and deserialization matches', () {
+    final rnd = Random();
+    getRandomInts(smallRepetition, 4294967295, rnd).forEach((length) {
+      final bytes = lengthToBytes(length);
+      test('$length -> $bytes', () async {
+        expect(bytes.length, 4);
+
+        final lengthDeserialized = lengthBytesToInt(bytes);
+
+        expect(length, lengthDeserialized);
+      });
+    });
+  });
+}