diff --git a/tests/web/deferred_function_types1_test.dart b/tests/web/deferred_function_types1_test.dart
index 91c907538f4..842521f2124 100644
--- a/tests/web/deferred_function_types1_test.dart
+++ b/tests/web/deferred_function_types1_test.dart
@@ -5,14 +5,17 @@
 // dart2jsOptions=--strong
 
 import 'package:expect/expect.dart';
+import 'package:async_helper/async_helper.dart';
 import 'deferred_function_types_lib1.dart' deferred as lib1;
 import 'deferred_function_types_lib2.dart' deferred as lib2;
 
-main() async {
-  await lib1.loadLibrary();
-  Expect.isTrue(lib1.method1() is int Function(int));
-  Expect.isFalse(lib1.method1() is String Function(String));
-  await lib2.loadLibrary();
-  Expect.isFalse(lib2.method2() is int Function(int));
-  Expect.isTrue(lib2.method2() is String Function(String));
+main() {
+  asyncTest(() async {
+    await lib1.loadLibrary();
+    Expect.isTrue(lib1.method1() is int Function(int));
+    Expect.isFalse(lib1.method1() is String Function(String));
+    await lib2.loadLibrary();
+    Expect.isFalse(lib2.method2() is int Function(int));
+    Expect.isTrue(lib2.method2() is String Function(String));
+  });
 }
diff --git a/tests/web/deferred_function_types2_test.dart b/tests/web/deferred_function_types2_test.dart
index 4336421b854..99e81a04934 100644
--- a/tests/web/deferred_function_types2_test.dart
+++ b/tests/web/deferred_function_types2_test.dart
@@ -4,15 +4,18 @@
 
 // dart2jsOptions=--strong
 
+import 'package:async_helper/async_helper.dart';
 import 'package:expect/expect.dart';
 import 'deferred_function_types_lib1.dart' deferred as lib1;
 import 'deferred_function_types_lib2.dart' deferred as lib2;
 
-main() async {
-  await lib2.loadLibrary();
-  Expect.isFalse(lib2.method2() is int Function(int));
-  Expect.isTrue(lib2.method2() is String Function(String));
-  await lib1.loadLibrary();
-  Expect.isTrue(lib1.method1() is int Function(int));
-  Expect.isFalse(lib1.method1() is String Function(String));
+main() {
+  asyncTest(() async {
+    await lib2.loadLibrary();
+    Expect.isFalse(lib2.method2() is int Function(int));
+    Expect.isTrue(lib2.method2() is String Function(String));
+    await lib1.loadLibrary();
+    Expect.isTrue(lib1.method1() is int Function(int));
+    Expect.isFalse(lib1.method1() is String Function(String));
+  });
 }
diff --git a/tests/web/deferred_function_types3_test.dart b/tests/web/deferred_function_types3_test.dart
index 98a6de8df91..ebd2eec49b7 100644
--- a/tests/web/deferred_function_types3_test.dart
+++ b/tests/web/deferred_function_types3_test.dart
@@ -4,15 +4,18 @@
 
 // dart2jsOptions=--strong
 
+import 'package:async_helper/async_helper.dart';
 import 'package:expect/expect.dart';
 import 'deferred_function_types_lib1.dart' deferred as lib1;
 import 'deferred_function_types_lib2.dart' deferred as lib2;
 
-main() async {
-  await lib1.loadLibrary();
-  Expect.isTrue(lib1.method3() is Object Function(Null));
-  Expect.isFalse(lib1.method3() is Object Function(Null, Null));
-  await lib2.loadLibrary();
-  Expect.isFalse(lib2.method4() is Object Function(Null));
-  Expect.isTrue(lib2.method4() is Object Function(Null, Null));
+main() {
+  asyncTest(() async {
+    await lib1.loadLibrary();
+    Expect.isTrue(lib1.method3() is Object? Function(Null));
+    Expect.isFalse(lib1.method3() is Object? Function(Null, Null));
+    await lib2.loadLibrary();
+    Expect.isFalse(lib2.method4() is Object? Function(Null));
+    Expect.isTrue(lib2.method4() is Object? Function(Null, Null));
+  });
 }
diff --git a/tests/web/deferred_function_types4_test.dart b/tests/web/deferred_function_types4_test.dart
index fc78d96a8bd..7577065d49c 100644
--- a/tests/web/deferred_function_types4_test.dart
+++ b/tests/web/deferred_function_types4_test.dart
@@ -4,15 +4,18 @@
 
 // dart2jsOptions=--strong
 
+import 'package:async_helper/async_helper.dart';
 import 'package:expect/expect.dart';
 import 'deferred_function_types_lib1.dart' deferred as lib1;
 import 'deferred_function_types_lib2.dart' deferred as lib2;
 
-main() async {
-  await lib2.loadLibrary();
-  Expect.isFalse(lib2.method4() is Object Function(Null));
-  Expect.isTrue(lib2.method4() is Object Function(Null, Null));
-  await lib1.loadLibrary();
-  Expect.isTrue(lib1.method3() is Object Function(Null));
-  Expect.isFalse(lib1.method3() is Object Function(Null, Null));
+main() {
+  asyncTest(() async {
+    await lib2.loadLibrary();
+    Expect.isFalse(lib2.method4() is Object? Function(Null));
+    Expect.isTrue(lib2.method4() is Object? Function(Null, Null));
+    await lib1.loadLibrary();
+    Expect.isTrue(lib1.method3() is Object? Function(Null));
+    Expect.isFalse(lib1.method3() is Object? Function(Null, Null));
+  });
 }
diff --git a/tests/web/deferred_function_types5_test.dart b/tests/web/deferred_function_types5_test.dart
index 998d678ba49..da9019690fa 100644
--- a/tests/web/deferred_function_types5_test.dart
+++ b/tests/web/deferred_function_types5_test.dart
@@ -4,15 +4,18 @@
 
 // dart2jsOptions=--strong
 
+import 'package:async_helper/async_helper.dart';
 import 'package:expect/expect.dart';
 import 'deferred_function_types_lib1.dart' deferred as lib1;
 import 'deferred_function_types_lib2.dart' deferred as lib2;
 
-main() async {
-  await lib1.loadLibrary();
-  Expect.isTrue(lib1.test3(lib1.method3()));
-  Expect.isFalse(lib1.method3() is Object Function(String));
-  await lib2.loadLibrary();
-  Expect.isFalse(lib2.method4() is Object Function(String, String));
-  Expect.isTrue(lib2.test4(lib2.method4()));
+main() {
+  asyncTest(() async {
+    await lib1.loadLibrary();
+    Expect.isTrue(lib1.test3(lib1.method3()));
+    Expect.isFalse(lib1.method3() is Object Function(String));
+    await lib2.loadLibrary();
+    Expect.isFalse(lib2.method4() is Object Function(String, String));
+    Expect.isTrue(lib2.test4(lib2.method4()));
+  });
 }
diff --git a/tests/web/deferred_function_types6_test.dart b/tests/web/deferred_function_types6_test.dart
index 2423b523276..d0d2b57eeb7 100644
--- a/tests/web/deferred_function_types6_test.dart
+++ b/tests/web/deferred_function_types6_test.dart
@@ -4,15 +4,18 @@
 
 // dart2jsOptions=--strong
 
+import 'package:async_helper/async_helper.dart';
 import 'package:expect/expect.dart';
 import 'deferred_function_types_lib1.dart' deferred as lib1;
 import 'deferred_function_types_lib2.dart' deferred as lib2;
 
-main() async {
-  await lib2.loadLibrary();
-  Expect.isFalse(lib2.method4() is Object Function(String, String));
-  Expect.isTrue(lib2.test4(lib2.method4()));
-  await lib1.loadLibrary();
-  Expect.isTrue(lib1.test3(lib1.method3()));
-  Expect.isFalse(lib1.method3() is Object Function(String));
+main() {
+  asyncTest(() async {
+    await lib2.loadLibrary();
+    Expect.isFalse(lib2.method4() is Object Function(String, String));
+    Expect.isTrue(lib2.test4(lib2.method4()));
+    await lib1.loadLibrary();
+    Expect.isTrue(lib1.test3(lib1.method3()));
+    Expect.isFalse(lib1.method3() is Object Function(String));
+  });
 }
diff --git a/tests/web/deferred_function_types7_test.dart b/tests/web/deferred_function_types7_test.dart
index fe7c49e1d7e..6627800eb24 100644
--- a/tests/web/deferred_function_types7_test.dart
+++ b/tests/web/deferred_function_types7_test.dart
@@ -5,20 +5,26 @@
 // dart2jsOptions=--strong
 
 import 'package:expect/expect.dart';
+import 'package:async_helper/async_helper.dart';
 import 'deferred_function_types_lib1.dart' deferred as lib1;
 import 'deferred_function_types_lib2.dart' deferred as lib2;
 
-main() async {
-  await lib1.loadLibrary();
-  Expect.isTrue(lib1.method1() is int Function(int));
-  Expect.isFalse(lib1.method1() is String Function(String));
-  Expect.isTrue(lib1.method5 is Object Function(Null, String, int));
-  Expect.isFalse(lib1.method5 is Object Function(Null, int, String));
-  Expect.isTrue(lib1.test5(lib1.method5));
-  await lib2.loadLibrary();
-  Expect.isFalse(lib2.method2() is int Function(int));
-  Expect.isTrue(lib2.method2() is String Function(String));
-  Expect.isFalse(lib2.method6 is Object Function(Null, String, int));
-  Expect.isTrue(lib2.method6 is Object Function(Null, int, String));
-  Expect.isTrue(lib2.test6(lib2.method6));
+@pragma('dart2js:never-inline')
+confuse(f) => f;
+
+main() {
+  asyncTest(() async {
+    await lib1.loadLibrary();
+    Expect.isTrue(lib1.method1() is int Function(int));
+    Expect.isFalse(lib1.method1() is String Function(String));
+    Expect.isTrue(confuse(lib1.method5) is Object? Function(Null, String, int));
+    Expect.isFalse(lib1.method5 is Object? Function(Null, int, String));
+    Expect.isTrue(lib1.test5(lib1.method5));
+    await lib2.loadLibrary();
+    Expect.isFalse(lib2.method2() is int Function(int));
+    Expect.isTrue(lib2.method2() is String Function(String));
+    Expect.isFalse(lib2.method6 is Object? Function(Null, String, int));
+    Expect.isTrue(confuse(lib2.method6) is Object? Function(Null, int, String));
+    Expect.isTrue(lib2.test6(lib2.method6));
+  });
 }
diff --git a/tests/web/deferred_function_types8_test.dart b/tests/web/deferred_function_types8_test.dart
index 7222ef5c257..859cd00c3f1 100644
--- a/tests/web/deferred_function_types8_test.dart
+++ b/tests/web/deferred_function_types8_test.dart
@@ -4,21 +4,27 @@
 
 // dart2jsOptions=--strong
 
+import 'package:async_helper/async_helper.dart';
 import 'package:expect/expect.dart';
 import 'deferred_function_types_lib1.dart' deferred as lib1;
 import 'deferred_function_types_lib2.dart' deferred as lib2;
 
-main() async {
-  await lib2.loadLibrary();
-  Expect.isFalse(lib2.method2() is int Function(int));
-  Expect.isTrue(lib2.method2() is String Function(String));
-  Expect.isFalse(lib2.method6 is Object Function(Null, String, int));
-  Expect.isTrue(lib2.method6 is Object Function(Null, int, String));
-  Expect.isTrue(lib2.test6(lib2.method6));
-  await lib1.loadLibrary();
-  Expect.isTrue(lib1.method1() is int Function(int));
-  Expect.isFalse(lib1.method1() is String Function(String));
-  Expect.isTrue(lib1.method5 is Object Function(Null, String, int));
-  Expect.isFalse(lib1.method5 is Object Function(Null, int, String));
-  Expect.isTrue(lib1.test5(lib1.method5));
+@pragma('dart2js:never-inline')
+confuse(f) => f;
+
+main() {
+  asyncTest(() async {
+    await lib2.loadLibrary();
+    Expect.isFalse(lib2.method2() is int Function(int));
+    Expect.isTrue(lib2.method2() is String Function(String));
+    Expect.isFalse(lib2.method6 is Object? Function(Null, String, int));
+    Expect.isTrue(confuse(lib2.method6) is Object? Function(Null, int, String));
+    Expect.isTrue(lib2.test6(lib2.method6));
+    await lib1.loadLibrary();
+    Expect.isTrue(lib1.method1() is int Function(int));
+    Expect.isFalse(lib1.method1() is String Function(String));
+    Expect.isTrue(confuse(lib1.method5) is Object? Function(Null, String, int));
+    Expect.isFalse(lib1.method5 is Object? Function(Null, int, String));
+    Expect.isTrue(lib1.test5(lib1.method5));
+  });
 }
diff --git a/tests/web/deferred_function_types_lib1.dart b/tests/web/deferred_function_types_lib1.dart
index 8a3a06f60d7..f94ba3e0a46 100644
--- a/tests/web/deferred_function_types_lib1.dart
+++ b/tests/web/deferred_function_types_lib1.dart
@@ -9,11 +9,11 @@ method1() {
 class Class1 {}
 
 method3() {
-  return (Class1 c) => c;
+  return (Class1? c) => c;
 }
 
-test3(o) => o is Class1 Function(Class1);
+test3(o) => o is Class1? Function(Class1?);
 
-method5(Class1 c, String s, int i) {}
+method5(Class1? c, String s, int i) {}
 
-test5(o) => o is Function(Class1, String, int);
+test5(o) => o is Function(Class1?, String, int);
diff --git a/tests/web/deferred_function_types_lib2.dart b/tests/web/deferred_function_types_lib2.dart
index a209dacd939..4df39cd53be 100644
--- a/tests/web/deferred_function_types_lib2.dart
+++ b/tests/web/deferred_function_types_lib2.dart
@@ -9,11 +9,11 @@ method2() {
 class Class2 {}
 
 method4() {
-  return (Class2 c1, Class2 c2) => c1;
+  return (Class2? c1, Class2? c2) => c1;
 }
 
-test4(o) => o is Class2 Function(Class2, Class2);
+test4(o) => o is Class2? Function(Class2?, Class2?);
 
-method6(Class2 c, int i, String s) {}
+method6(Class2? c, int i, String s) {}
 
-test6(o) => o is Function(Class2, int, String);
+test6(o) => o is Function(Class2?, int, String);
diff --git a/tests/web_2/deferred_function_types1_test.dart b/tests/web_2/deferred_function_types1_test.dart
index 2e853e1ca06..607c1407e9f 100644
--- a/tests/web_2/deferred_function_types1_test.dart
+++ b/tests/web_2/deferred_function_types1_test.dart
@@ -6,15 +6,18 @@
 
 // dart2jsOptions=--strong
 
+import 'package:async_helper/async_helper.dart';
 import 'package:expect/expect.dart';
 import 'deferred_function_types_lib1.dart' deferred as lib1;
 import 'deferred_function_types_lib2.dart' deferred as lib2;
 
-main() async {
-  await lib1.loadLibrary();
-  Expect.isTrue(lib1.method1() is int Function(int));
-  Expect.isFalse(lib1.method1() is String Function(String));
-  await lib2.loadLibrary();
-  Expect.isFalse(lib2.method2() is int Function(int));
-  Expect.isTrue(lib2.method2() is String Function(String));
+main() {
+  asyncTest(() async {
+    await lib1.loadLibrary();
+    Expect.isTrue(lib1.method1() is int Function(int));
+    Expect.isFalse(lib1.method1() is String Function(String));
+    await lib2.loadLibrary();
+    Expect.isFalse(lib2.method2() is int Function(int));
+    Expect.isTrue(lib2.method2() is String Function(String));
+  });
 }
diff --git a/tests/web_2/deferred_function_types2_test.dart b/tests/web_2/deferred_function_types2_test.dart
index 586e1b8dcf7..087996efa31 100644
--- a/tests/web_2/deferred_function_types2_test.dart
+++ b/tests/web_2/deferred_function_types2_test.dart
@@ -6,15 +6,18 @@
 
 // dart2jsOptions=--strong
 
+import 'package:async_helper/async_helper.dart';
 import 'package:expect/expect.dart';
 import 'deferred_function_types_lib1.dart' deferred as lib1;
 import 'deferred_function_types_lib2.dart' deferred as lib2;
 
-main() async {
-  await lib2.loadLibrary();
-  Expect.isFalse(lib2.method2() is int Function(int));
-  Expect.isTrue(lib2.method2() is String Function(String));
-  await lib1.loadLibrary();
-  Expect.isTrue(lib1.method1() is int Function(int));
-  Expect.isFalse(lib1.method1() is String Function(String));
+main() {
+  asyncTest(() async {
+    await lib2.loadLibrary();
+    Expect.isFalse(lib2.method2() is int Function(int));
+    Expect.isTrue(lib2.method2() is String Function(String));
+    await lib1.loadLibrary();
+    Expect.isTrue(lib1.method1() is int Function(int));
+    Expect.isFalse(lib1.method1() is String Function(String));
+  });
 }
diff --git a/tests/web_2/deferred_function_types3_test.dart b/tests/web_2/deferred_function_types3_test.dart
index 10d69f47d8a..06968223f26 100644
--- a/tests/web_2/deferred_function_types3_test.dart
+++ b/tests/web_2/deferred_function_types3_test.dart
@@ -6,15 +6,18 @@
 
 // dart2jsOptions=--strong
 
+import 'package:async_helper/async_helper.dart';
 import 'package:expect/expect.dart';
 import 'deferred_function_types_lib1.dart' deferred as lib1;
 import 'deferred_function_types_lib2.dart' deferred as lib2;
 
-main() async {
-  await lib1.loadLibrary();
-  Expect.isTrue(lib1.method3() is Object Function(Null));
-  Expect.isFalse(lib1.method3() is Object Function(Null, Null));
-  await lib2.loadLibrary();
-  Expect.isFalse(lib2.method4() is Object Function(Null));
-  Expect.isTrue(lib2.method4() is Object Function(Null, Null));
+main() {
+  asyncTest(() async {
+    await lib1.loadLibrary();
+    Expect.isTrue(lib1.method3() is Object Function(Null));
+    Expect.isFalse(lib1.method3() is Object Function(Null, Null));
+    await lib2.loadLibrary();
+    Expect.isFalse(lib2.method4() is Object Function(Null));
+    Expect.isTrue(lib2.method4() is Object Function(Null, Null));
+  });
 }
diff --git a/tests/web_2/deferred_function_types4_test.dart b/tests/web_2/deferred_function_types4_test.dart
index 27fedbc9330..3277948001c 100644
--- a/tests/web_2/deferred_function_types4_test.dart
+++ b/tests/web_2/deferred_function_types4_test.dart
@@ -6,15 +6,18 @@
 
 // dart2jsOptions=--strong
 
+import 'package:async_helper/async_helper.dart';
 import 'package:expect/expect.dart';
 import 'deferred_function_types_lib1.dart' deferred as lib1;
 import 'deferred_function_types_lib2.dart' deferred as lib2;
 
-main() async {
-  await lib2.loadLibrary();
-  Expect.isFalse(lib2.method4() is Object Function(Null));
-  Expect.isTrue(lib2.method4() is Object Function(Null, Null));
-  await lib1.loadLibrary();
-  Expect.isTrue(lib1.method3() is Object Function(Null));
-  Expect.isFalse(lib1.method3() is Object Function(Null, Null));
+main() {
+  asyncTest(() async {
+    await lib2.loadLibrary();
+    Expect.isFalse(lib2.method4() is Object Function(Null));
+    Expect.isTrue(lib2.method4() is Object Function(Null, Null));
+    await lib1.loadLibrary();
+    Expect.isTrue(lib1.method3() is Object Function(Null));
+    Expect.isFalse(lib1.method3() is Object Function(Null, Null));
+  });
 }
diff --git a/tests/web_2/deferred_function_types5_test.dart b/tests/web_2/deferred_function_types5_test.dart
index 75b04e3285e..33fb076bcd8 100644
--- a/tests/web_2/deferred_function_types5_test.dart
+++ b/tests/web_2/deferred_function_types5_test.dart
@@ -6,15 +6,18 @@
 
 // dart2jsOptions=--strong
 
+import 'package:async_helper/async_helper.dart';
 import 'package:expect/expect.dart';
 import 'deferred_function_types_lib1.dart' deferred as lib1;
 import 'deferred_function_types_lib2.dart' deferred as lib2;
 
-main() async {
-  await lib1.loadLibrary();
-  Expect.isTrue(lib1.test3(lib1.method3()));
-  Expect.isFalse(lib1.method3() is Object Function(String));
-  await lib2.loadLibrary();
-  Expect.isFalse(lib2.method4() is Object Function(String, String));
-  Expect.isTrue(lib2.test4(lib2.method4()));
+main() {
+  asyncTest(() async {
+    await lib1.loadLibrary();
+    Expect.isTrue(lib1.test3(lib1.method3()));
+    Expect.isFalse(lib1.method3() is Object Function(String));
+    await lib2.loadLibrary();
+    Expect.isFalse(lib2.method4() is Object Function(String, String));
+    Expect.isTrue(lib2.test4(lib2.method4()));
+  });
 }
diff --git a/tests/web_2/deferred_function_types6_test.dart b/tests/web_2/deferred_function_types6_test.dart
index 0a1b2a7921c..14105a984d8 100644
--- a/tests/web_2/deferred_function_types6_test.dart
+++ b/tests/web_2/deferred_function_types6_test.dart
@@ -6,15 +6,18 @@
 
 // dart2jsOptions=--strong
 
+import 'package:async_helper/async_helper.dart';
 import 'package:expect/expect.dart';
 import 'deferred_function_types_lib1.dart' deferred as lib1;
 import 'deferred_function_types_lib2.dart' deferred as lib2;
 
-main() async {
-  await lib2.loadLibrary();
-  Expect.isFalse(lib2.method4() is Object Function(String, String));
-  Expect.isTrue(lib2.test4(lib2.method4()));
-  await lib1.loadLibrary();
-  Expect.isTrue(lib1.test3(lib1.method3()));
-  Expect.isFalse(lib1.method3() is Object Function(String));
+main() {
+  asyncTest(() async {
+    await lib2.loadLibrary();
+    Expect.isFalse(lib2.method4() is Object Function(String, String));
+    Expect.isTrue(lib2.test4(lib2.method4()));
+    await lib1.loadLibrary();
+    Expect.isTrue(lib1.test3(lib1.method3()));
+    Expect.isFalse(lib1.method3() is Object Function(String));
+  });
 }
diff --git a/tests/web_2/deferred_function_types7_test.dart b/tests/web_2/deferred_function_types7_test.dart
index ba16f2eecd9..38163a589bd 100644
--- a/tests/web_2/deferred_function_types7_test.dart
+++ b/tests/web_2/deferred_function_types7_test.dart
@@ -6,21 +6,24 @@
 
 // dart2jsOptions=--strong
 
+import 'package:async_helper/async_helper.dart';
 import 'package:expect/expect.dart';
 import 'deferred_function_types_lib1.dart' deferred as lib1;
 import 'deferred_function_types_lib2.dart' deferred as lib2;
 
-main() async {
-  await lib1.loadLibrary();
-  Expect.isTrue(lib1.method1() is int Function(int));
-  Expect.isFalse(lib1.method1() is String Function(String));
-  Expect.isTrue(lib1.method5 is Object Function(Null, String, int));
-  Expect.isFalse(lib1.method5 is Object Function(Null, int, String));
-  Expect.isTrue(lib1.test5(lib1.method5));
-  await lib2.loadLibrary();
-  Expect.isFalse(lib2.method2() is int Function(int));
-  Expect.isTrue(lib2.method2() is String Function(String));
-  Expect.isFalse(lib2.method6 is Object Function(Null, String, int));
-  Expect.isTrue(lib2.method6 is Object Function(Null, int, String));
-  Expect.isTrue(lib2.test6(lib2.method6));
+main() {
+  asyncTest(() async {
+    await lib1.loadLibrary();
+    Expect.isTrue(lib1.method1() is int Function(int));
+    Expect.isFalse(lib1.method1() is String Function(String));
+    Expect.isTrue(lib1.method5 is Object Function(Null, String, int));
+    Expect.isFalse(lib1.method5 is Object Function(Null, int, String));
+    Expect.isTrue(lib1.test5(lib1.method5));
+    await lib2.loadLibrary();
+    Expect.isFalse(lib2.method2() is int Function(int));
+    Expect.isTrue(lib2.method2() is String Function(String));
+    Expect.isFalse(lib2.method6 is Object Function(Null, String, int));
+    Expect.isTrue(lib2.method6 is Object Function(Null, int, String));
+    Expect.isTrue(lib2.test6(lib2.method6));
+  });
 }
diff --git a/tests/web_2/deferred_function_types8_test.dart b/tests/web_2/deferred_function_types8_test.dart
index f6624a1dfbd..35abeb84f33 100644
--- a/tests/web_2/deferred_function_types8_test.dart
+++ b/tests/web_2/deferred_function_types8_test.dart
@@ -6,21 +6,24 @@
 
 // dart2jsOptions=--strong
 
+import 'package:async_helper/async_helper.dart';
 import 'package:expect/expect.dart';
 import 'deferred_function_types_lib1.dart' deferred as lib1;
 import 'deferred_function_types_lib2.dart' deferred as lib2;
 
-main() async {
-  await lib2.loadLibrary();
-  Expect.isFalse(lib2.method2() is int Function(int));
-  Expect.isTrue(lib2.method2() is String Function(String));
-  Expect.isFalse(lib2.method6 is Object Function(Null, String, int));
-  Expect.isTrue(lib2.method6 is Object Function(Null, int, String));
-  Expect.isTrue(lib2.test6(lib2.method6));
-  await lib1.loadLibrary();
-  Expect.isTrue(lib1.method1() is int Function(int));
-  Expect.isFalse(lib1.method1() is String Function(String));
-  Expect.isTrue(lib1.method5 is Object Function(Null, String, int));
-  Expect.isFalse(lib1.method5 is Object Function(Null, int, String));
-  Expect.isTrue(lib1.test5(lib1.method5));
+main() {
+  asyncTest(() async {
+    await lib2.loadLibrary();
+    Expect.isFalse(lib2.method2() is int Function(int));
+    Expect.isTrue(lib2.method2() is String Function(String));
+    Expect.isFalse(lib2.method6 is Object Function(Null, String, int));
+    Expect.isTrue(lib2.method6 is Object Function(Null, int, String));
+    Expect.isTrue(lib2.test6(lib2.method6));
+    await lib1.loadLibrary();
+    Expect.isTrue(lib1.method1() is int Function(int));
+    Expect.isFalse(lib1.method1() is String Function(String));
+    Expect.isTrue(lib1.method5 is Object Function(Null, String, int));
+    Expect.isFalse(lib1.method5 is Object Function(Null, int, String));
+    Expect.isTrue(lib1.test5(lib1.method5));
+  });
 }