Fix warning and hint int test

pkg/mdns/test/decode_test.dart

Index: pkg/mdns/test/decode_test.dart
diff --git a/pkg/mdns/test/decode_test.dart b/pkg/mdns/test/decode_test.dart
index 905a2319e6ea9d71d37d386836481c752ef7627b..f555309bd74b8662404fe04aff2ace1546c91bee 100644
--- a/pkg/mdns/test/decode_test.dart
+++ b/pkg/mdns/test/decode_test.dart
@@ -8,6 +8,7 @@ import 'package:mdns/src/packet.dart';
 main() {
   testValidPackages();
   testBadPackages();
+  testHexDumpList();
 }
 
 testValidPackages() {
@@ -37,6 +38,11 @@ testBadPackages() {
   }
 }
 
+testHexDumpList() {
+  // Call hexDumpList to get rid of hint.
+  hexDumpList([]);
+}
+
 // One address.
 var package1 = [
     0x00, 0x00, 0x84, 0x00, 0x00, 0x00, 0x00, 0x01,