Parse comma-separated multiple values.

test/args_test.dart

Index: test/args_test.dart
diff --git a/test/args_test.dart b/test/args_test.dart
index 4c23ba5338455139dbd18a1c25492f448d41d0c4..b22d0c95338f7bc2528d2fe607e5affd9a42cebc 100644
--- a/test/args_test.dart
+++ b/test/args_test.dart
@@ -109,6 +109,13 @@ void main() {
       }
     });
 
+    test('throws ArgumentError if splitCommas is passed with allowMultiple: '
+        'false', () {
+      var parser = new ArgParser();
+      throwsIllegalArg(() => parser.addOption('flummox', splitCommas: true));
+      throwsIllegalArg(() => parser.addOption('flummox', splitCommas: false));
+    });
+
     test('accepts valid option names', () {
       var parser = new ArgParser();