Dart Duration.toString() demo

main.dart

void main() {
  // Expected: -0:00:00.000123
  // Actual:   0:00:00.000123
  print(Duration(microseconds: -123));
  
  // Expected: -0:30:00.000000
  // Actual:   0:30:00.000000
  print(Duration(minutes: -30));

  // Expected: -1:00:00.000000
  // Actual:   -1:00.00.00-0.0 (JS/DartPad only)
  print(Duration(hours: -1));
}