Fix, take 3

pkg/web_components/test/interop_test.dart

Index: pkg/web_components/test/interop_test.dart
diff --git a/pkg/web_components/test/interop_test.dart b/pkg/web_components/test/interop_test.dart
index d7b7a0139e04ab023d95b7b90c1ee6f035ab3cba..64dfb6426f7bc673fb130653e803f77640f12390 100644
--- a/pkg/web_components/test/interop_test.dart
+++ b/pkg/web_components/test/interop_test.dart
@@ -12,13 +12,15 @@ import 'package:unittest/unittest.dart';
 import 'package:web_components/interop.dart';
 import 'package:web_components/polyfill.dart';
 
-main() {
-  useHtmlConfiguration();
-  setUp(() => customElementsReady.then((_) {
+final globalSetup = customElementsReady.then((_) {
     registerDartType('x-a', XAWrapper);
     registerDartType('x-b', XBWrapper, extendsTag: 'div');
     registerDartType('x-c', XCWrapper);
-  }));
+  });
+
+main() {
+  useHtmlConfiguration();
+  setUp(() => globalSetup);
 
   test('interop is supported', () {
     expect(isSupported, isTrue);