remove magic calculations in send progress test

dio/test/upload_test.dart

@@ -101,29 +101,30 @@ void main() {
   test('send progress', () async {
     final data = <Uint8List>[
       Uint8List.fromList([10, 1]),
-      Uint8List.fromList([1, 4]),
+      Uint8List.fromList([1, 4, 5]),
       Uint8List.fromList([5, 1]),
       Uint8List.fromList([1, 1]),
       Uint8List.fromList([2, 4]),
     ];
     final stream = Stream.fromIterable(data);
+    final expanded = data.expand((element) => element);
     final List<int> collected = [];
     final _ = await dio.put(
       '/put',
       data: stream,
       onSendProgress: (a, b) {
-        expect(b, 10);
+        expect(b, expanded.length);
         collected.add(a);
       },
       options: Options(
         contentType: Headers.textPlainContentType,
         headers: {
-          Headers.contentLengthHeader: data.length * 2, // set content-length
+          Headers.contentLengthHeader: expanded.length, // set content-length
         },
       ),
     );
     for (int i = 0; i < data.length; i++) {
-      expect(collected[i], (i + 1) * 2);
+      expect(collected[i], data.sublist(0, i + 1).expand((e) => e).length);
     }
   });
 }