pkg/args: a bunch of test cleanup

pkg/args/test/parse_all_test.dart

Index: pkg/args/test/parse_all_test.dart
diff --git a/pkg/args/test/parse_all_test.dart b/pkg/args/test/parse_all_test.dart
index 8498ae672c63da31b5f40868a260970ed279d941..d404c2f906c209a824ede715d639cf515f871d91 100644
--- a/pkg/args/test/parse_all_test.dart
+++ b/pkg/args/test/parse_all_test.dart
@@ -7,7 +7,7 @@ library parse_all_test;
 import 'package:unittest/unittest.dart';
 import 'package:args/args.dart';
 
-main() {
+void main() {
   group('ArgParser.parse(allowTrailingOptions: true) '
         'starting with a non-option', () {
     test('followed by flag', () {
@@ -57,7 +57,8 @@ main() {
     });
   });
 }
-expectThrows(ArgParser parser, List<String> args) =>
+
+void expectThrows(ArgParser parser, List<String> args) =>
   expect(() => parser.parse(args, allowTrailingOptions: true),
       throwsFormatException,
       reason: "with allowTrailingOptions: true");