diff --git a/tests/language/async_nested/async_nested01_test.dart b/tests/language/async_nested/async_nested01_test.dart
new file mode 100644
index 00000000000..4369751e780
--- /dev/null
+++ b/tests/language/async_nested/async_nested01_test.dart
@@ -0,0 +1,46 @@
+// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// This has been automatically generated by script
+// "async_nested_test_generator.dart".
+
+import 'dart:async';
+
+void main() async {
+  String expected = "1 2 3 4 5 6 7 8 9 10";
+  Node node = new Node('1', [
+    new Node('2', []),
+    await new Future.value(new Node('3', [
+      await new Future.value(new Node('4', [
+        new Node('5', [
+          await new Future.value(new Node('6', [
+            await new Future.value(new Node('7', [])),
+          ])),
+          await new Future.value(new Node('8', [])),
+          await new Future.value(new Node('9', [])),
+        ]),
+      ])),
+    ])),
+    await new Future.value(new Node('10', [])),
+  ]);
+  String actual = node.toSimpleString();
+  print(actual);
+  if (actual != expected) {
+    throw "Expected '$expected' but got '$actual'";
+  }
+}
+
+class Node {
+  final List<Node>? nested;
+  final String name;
+
+  Node(this.name, [this.nested]) {}
+
+  String toString() => '<$name:[${nested?.join(', ')}]>';
+
+  toSimpleString() {
+    var tmp = nested?.map((child) => child.toSimpleString());
+    return '$name ${tmp?.join(' ')}'.trim();
+  }
+}
diff --git a/tests/language/async_nested/async_nested02_test.dart b/tests/language/async_nested/async_nested02_test.dart
new file mode 100644
index 00000000000..0d98bcc4e18
--- /dev/null
+++ b/tests/language/async_nested/async_nested02_test.dart
@@ -0,0 +1,46 @@
+// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// This has been automatically generated by script
+// "async_nested_test_generator.dart".
+
+import 'dart:async';
+
+void main() async {
+  String expected = "1 2 3 4 5 6 7 8 9 10 11";
+  Node node = new Node('1', [
+    new Node('2', [
+      new Node('3', []),
+    ]),
+    await new Future.value(new Node('4', [
+      await new Future.value(new Node('5', [])),
+      new Node('6', [
+        new Node('7', []),
+        await new Future.value(new Node('8', [])),
+      ]),
+      await new Future.value(new Node('9', [])),
+    ])),
+    await new Future.value(new Node('10', [])),
+    new Node('11', []),
+  ]);
+  String actual = node.toSimpleString();
+  print(actual);
+  if (actual != expected) {
+    throw "Expected '$expected' but got '$actual'";
+  }
+}
+
+class Node {
+  final List<Node>? nested;
+  final String name;
+
+  Node(this.name, [this.nested]) {}
+
+  String toString() => '<$name:[${nested?.join(', ')}]>';
+
+  toSimpleString() {
+    var tmp = nested?.map((child) => child.toSimpleString());
+    return '$name ${tmp?.join(' ')}'.trim();
+  }
+}
diff --git a/tests/language/async_nested/async_nested03_test.dart b/tests/language/async_nested/async_nested03_test.dart
new file mode 100644
index 00000000000..1fc44f52f60
--- /dev/null
+++ b/tests/language/async_nested/async_nested03_test.dart
@@ -0,0 +1,48 @@
+// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// This has been automatically generated by script
+// "async_nested_test_generator.dart".
+
+import 'dart:async';
+
+void main() async {
+  String expected = "1 2 3 4 5 6 7 8 9 10 11 12";
+  Node node = new Node('1', [
+    new Node('2', [
+      await new Future.value(new Node('3', [])),
+      await new Future.value(new Node('4', [
+        new Node('5', []),
+        await new Future.value(new Node('6', [])),
+        await new Future.value(new Node('7', [])),
+        new Node('8', []),
+      ])),
+      new Node('9', []),
+      new Node('10', [
+        new Node('11', [
+          await new Future.value(new Node('12', [])),
+        ]),
+      ]),
+    ]),
+  ]);
+  String actual = node.toSimpleString();
+  print(actual);
+  if (actual != expected) {
+    throw "Expected '$expected' but got '$actual'";
+  }
+}
+
+class Node {
+  final List<Node>? nested;
+  final String name;
+
+  Node(this.name, [this.nested]) {}
+
+  String toString() => '<$name:[${nested?.join(', ')}]>';
+
+  toSimpleString() {
+    var tmp = nested?.map((child) => child.toSimpleString());
+    return '$name ${tmp?.join(' ')}'.trim();
+  }
+}
diff --git a/tests/language/async_nested/async_nested04_test.dart b/tests/language/async_nested/async_nested04_test.dart
new file mode 100644
index 00000000000..6cbbef278ea
--- /dev/null
+++ b/tests/language/async_nested/async_nested04_test.dart
@@ -0,0 +1,46 @@
+// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// This has been automatically generated by script
+// "async_nested_test_generator.dart".
+
+import 'dart:async';
+
+void main() async {
+  String expected = "1 2 3 4 5 6 7 8 9 10 11 12";
+  Node node = await new Future.value(new Node('1', [
+    await new Future.value(new Node('2', [])),
+    await new Future.value(new Node('3', [])),
+    await new Future.value(new Node('4', [
+      await new Future.value(new Node('5', [])),
+      new Node('6', []),
+      new Node('7', [
+        new Node('8', []),
+        await new Future.value(new Node('9', [])),
+      ]),
+      await new Future.value(new Node('10', [])),
+    ])),
+    new Node('11', []),
+    await new Future.value(new Node('12', [])),
+  ]));
+  String actual = node.toSimpleString();
+  print(actual);
+  if (actual != expected) {
+    throw "Expected '$expected' but got '$actual'";
+  }
+}
+
+class Node {
+  final List<Node>? nested;
+  final String name;
+
+  Node(this.name, [this.nested]) {}
+
+  String toString() => '<$name:[${nested?.join(', ')}]>';
+
+  toSimpleString() {
+    var tmp = nested?.map((child) => child.toSimpleString());
+    return '$name ${tmp?.join(' ')}'.trim();
+  }
+}
diff --git a/tests/language/async_nested/async_nested05_test.dart b/tests/language/async_nested/async_nested05_test.dart
new file mode 100644
index 00000000000..b57f225f3dc
--- /dev/null
+++ b/tests/language/async_nested/async_nested05_test.dart
@@ -0,0 +1,46 @@
+// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// This has been automatically generated by script
+// "async_nested_test_generator.dart".
+
+import 'dart:async';
+
+void main() async {
+  String expected = "1 2 3 4 5 6 7 8 9 10 11 12";
+  Node node = await new Future.value(new Node('1', [
+    await new Future.value(new Node('2', [])),
+    await new Future.value(new Node('3', [
+      await new Future.value(new Node('4', [])),
+      await new Future.value(new Node('5', [])),
+      await new Future.value(new Node('6', [])),
+    ])),
+    new Node('7', []),
+    new Node('8', [
+      new Node('9', []),
+      await new Future.value(new Node('10', [])),
+      new Node('11', []),
+      await new Future.value(new Node('12', [])),
+    ]),
+  ]));
+  String actual = node.toSimpleString();
+  print(actual);
+  if (actual != expected) {
+    throw "Expected '$expected' but got '$actual'";
+  }
+}
+
+class Node {
+  final List<Node>? nested;
+  final String name;
+
+  Node(this.name, [this.nested]) {}
+
+  String toString() => '<$name:[${nested?.join(', ')}]>';
+
+  toSimpleString() {
+    var tmp = nested?.map((child) => child.toSimpleString());
+    return '$name ${tmp?.join(' ')}'.trim();
+  }
+}
diff --git a/tests/language/async_nested/async_nested06_test.dart b/tests/language/async_nested/async_nested06_test.dart
new file mode 100644
index 00000000000..70eb9c98217
--- /dev/null
+++ b/tests/language/async_nested/async_nested06_test.dart
@@ -0,0 +1,49 @@
+// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// This has been automatically generated by script
+// "async_nested_test_generator.dart".
+
+import 'dart:async';
+
+void main() async {
+  String expected = "1 2 3 4 5 6 7 8 9 10 11 12";
+  Node node = new Node('1', [
+    new Node('2', [
+      await new Future.value(new Node('3', [
+        new Node('4', []),
+      ])),
+      new Node('5', [
+        await new Future.value(new Node('6', [
+          await new Future.value(new Node('7', [
+            new Node('8', []),
+          ])),
+          new Node('9', []),
+          await new Future.value(new Node('10', [])),
+        ])),
+        await new Future.value(new Node('11', [])),
+        await new Future.value(new Node('12', [])),
+      ]),
+    ]),
+  ]);
+  String actual = node.toSimpleString();
+  print(actual);
+  if (actual != expected) {
+    throw "Expected '$expected' but got '$actual'";
+  }
+}
+
+class Node {
+  final List<Node>? nested;
+  final String name;
+
+  Node(this.name, [this.nested]) {}
+
+  String toString() => '<$name:[${nested?.join(', ')}]>';
+
+  toSimpleString() {
+    var tmp = nested?.map((child) => child.toSimpleString());
+    return '$name ${tmp?.join(' ')}'.trim();
+  }
+}
diff --git a/tests/language/async_nested/async_nested07_test.dart b/tests/language/async_nested/async_nested07_test.dart
new file mode 100644
index 00000000000..5c93a6d98c5
--- /dev/null
+++ b/tests/language/async_nested/async_nested07_test.dart
@@ -0,0 +1,48 @@
+// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// This has been automatically generated by script
+// "async_nested_test_generator.dart".
+
+import 'dart:async';
+
+void main() async {
+  String expected = "1 2 3 4 5 6 7 8 9 10 11 12";
+  Node node = await new Future.value(new Node('1', [
+    await new Future.value(new Node('2', [])),
+    await new Future.value(new Node('3', [
+      new Node('4', []),
+      new Node('5', []),
+      await new Future.value(new Node('6', [])),
+      new Node('7', [
+        await new Future.value(new Node('8', [
+          new Node('9', []),
+        ])),
+        await new Future.value(new Node('10', [])),
+      ]),
+    ])),
+    new Node('11', [
+      await new Future.value(new Node('12', [])),
+    ]),
+  ]));
+  String actual = node.toSimpleString();
+  print(actual);
+  if (actual != expected) {
+    throw "Expected '$expected' but got '$actual'";
+  }
+}
+
+class Node {
+  final List<Node>? nested;
+  final String name;
+
+  Node(this.name, [this.nested]) {}
+
+  String toString() => '<$name:[${nested?.join(', ')}]>';
+
+  toSimpleString() {
+    var tmp = nested?.map((child) => child.toSimpleString());
+    return '$name ${tmp?.join(' ')}'.trim();
+  }
+}
diff --git a/tests/language/async_nested/async_nested08_test.dart b/tests/language/async_nested/async_nested08_test.dart
new file mode 100644
index 00000000000..170a7355bb7
--- /dev/null
+++ b/tests/language/async_nested/async_nested08_test.dart
@@ -0,0 +1,48 @@
+// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// This has been automatically generated by script
+// "async_nested_test_generator.dart".
+
+import 'dart:async';
+
+void main() async {
+  String expected = "1 2 3 4 5 6 7 8 9 10 11 12 13";
+  Node node = await new Future.value(new Node('1', [
+    await new Future.value(new Node('2', [
+      await new Future.value(new Node('3', [])),
+    ])),
+    await new Future.value(new Node('4', [
+      await new Future.value(new Node('5', [])),
+      await new Future.value(new Node('6', [])),
+      new Node('7', []),
+      new Node('8', []),
+      new Node('9', [
+        await new Future.value(new Node('10', [])),
+      ]),
+      new Node('11', []),
+      new Node('12', []),
+    ])),
+    await new Future.value(new Node('13', [])),
+  ]));
+  String actual = node.toSimpleString();
+  print(actual);
+  if (actual != expected) {
+    throw "Expected '$expected' but got '$actual'";
+  }
+}
+
+class Node {
+  final List<Node>? nested;
+  final String name;
+
+  Node(this.name, [this.nested]) {}
+
+  String toString() => '<$name:[${nested?.join(', ')}]>';
+
+  toSimpleString() {
+    var tmp = nested?.map((child) => child.toSimpleString());
+    return '$name ${tmp?.join(' ')}'.trim();
+  }
+}
diff --git a/tests/language/async_nested/async_nested09_test.dart b/tests/language/async_nested/async_nested09_test.dart
new file mode 100644
index 00000000000..f44e7253e3e
--- /dev/null
+++ b/tests/language/async_nested/async_nested09_test.dart
@@ -0,0 +1,49 @@
+// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// This has been automatically generated by script
+// "async_nested_test_generator.dart".
+
+import 'dart:async';
+
+void main() async {
+  String expected = "1 2 3 4 5 6 7 8 9 10 11 12 13";
+  Node node = new Node('1', [
+    new Node('2', [
+      await new Future.value(new Node('3', [])),
+      await new Future.value(new Node('4', [
+        new Node('5', []),
+        new Node('6', []),
+        new Node('7', []),
+        new Node('8', []),
+        await new Future.value(new Node('9', [
+          new Node('10', [
+            new Node('11', []),
+          ]),
+        ])),
+        await new Future.value(new Node('12', [])),
+      ])),
+      await new Future.value(new Node('13', [])),
+    ]),
+  ]);
+  String actual = node.toSimpleString();
+  print(actual);
+  if (actual != expected) {
+    throw "Expected '$expected' but got '$actual'";
+  }
+}
+
+class Node {
+  final List<Node>? nested;
+  final String name;
+
+  Node(this.name, [this.nested]) {}
+
+  String toString() => '<$name:[${nested?.join(', ')}]>';
+
+  toSimpleString() {
+    var tmp = nested?.map((child) => child.toSimpleString());
+    return '$name ${tmp?.join(' ')}'.trim();
+  }
+}
diff --git a/tests/language/async_nested/async_nested10_test.dart b/tests/language/async_nested/async_nested10_test.dart
new file mode 100644
index 00000000000..419d36a9c26
--- /dev/null
+++ b/tests/language/async_nested/async_nested10_test.dart
@@ -0,0 +1,51 @@
+// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// This has been automatically generated by script
+// "async_nested_test_generator.dart".
+
+import 'dart:async';
+
+void main() async {
+  String expected = "1 2 3 4 5 6 7 8 9 10 11 12 13";
+  Node node = new Node('1', [
+    await new Future.value(new Node('2', [
+      new Node('3', []),
+      await new Future.value(new Node('4', [
+        await new Future.value(new Node('5', [
+          new Node('6', []),
+          new Node('7', [
+            new Node('8', []),
+          ]),
+          await new Future.value(new Node('9', [])),
+          new Node('10', [
+            new Node('11', []),
+          ]),
+        ])),
+      ])),
+      await new Future.value(new Node('12', [
+        new Node('13', []),
+      ])),
+    ])),
+  ]);
+  String actual = node.toSimpleString();
+  print(actual);
+  if (actual != expected) {
+    throw "Expected '$expected' but got '$actual'";
+  }
+}
+
+class Node {
+  final List<Node>? nested;
+  final String name;
+
+  Node(this.name, [this.nested]) {}
+
+  String toString() => '<$name:[${nested?.join(', ')}]>';
+
+  toSimpleString() {
+    var tmp = nested?.map((child) => child.toSimpleString());
+    return '$name ${tmp?.join(' ')}'.trim();
+  }
+}
diff --git a/tests/language/async_nested/async_nested11_test.dart b/tests/language/async_nested/async_nested11_test.dart
new file mode 100644
index 00000000000..4349917839a
--- /dev/null
+++ b/tests/language/async_nested/async_nested11_test.dart
@@ -0,0 +1,50 @@
+// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// This has been automatically generated by script
+// "async_nested_test_generator.dart".
+
+import 'dart:async';
+
+void main() async {
+  String expected = "1 2 3 4 5 6 7 8 9 10 11 12 13";
+  Node node = await new Future.value(new Node('1', [
+    await new Future.value(new Node('2', [
+      new Node('3', []),
+      new Node('4', [
+        new Node('5', []),
+        new Node('6', []),
+        await new Future.value(new Node('7', [
+          new Node('8', [
+            new Node('9', []),
+          ]),
+          new Node('10', []),
+          new Node('11', [
+            await new Future.value(new Node('12', [])),
+          ]),
+        ])),
+        await new Future.value(new Node('13', [])),
+      ]),
+    ])),
+  ]));
+  String actual = node.toSimpleString();
+  print(actual);
+  if (actual != expected) {
+    throw "Expected '$expected' but got '$actual'";
+  }
+}
+
+class Node {
+  final List<Node>? nested;
+  final String name;
+
+  Node(this.name, [this.nested]) {}
+
+  String toString() => '<$name:[${nested?.join(', ')}]>';
+
+  toSimpleString() {
+    var tmp = nested?.map((child) => child.toSimpleString());
+    return '$name ${tmp?.join(' ')}'.trim();
+  }
+}
diff --git a/tests/language/async_nested/async_nested12_test.dart b/tests/language/async_nested/async_nested12_test.dart
new file mode 100644
index 00000000000..cf6a305edcf
--- /dev/null
+++ b/tests/language/async_nested/async_nested12_test.dart
@@ -0,0 +1,49 @@
+// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// This has been automatically generated by script
+// "async_nested_test_generator.dart".
+
+import 'dart:async';
+
+void main() async {
+  String expected = "1 2 3 4 5 6 7 8 9 10 11 12 13";
+  Node node = new Node('1', [
+    await new Future.value(new Node('2', [])),
+    await new Future.value(new Node('3', [])),
+    new Node('4', [
+      await new Future.value(new Node('5', [
+        new Node('6', []),
+        new Node('7', []),
+        await new Future.value(new Node('8', [
+          new Node('9', []),
+        ])),
+      ])),
+      new Node('10', [
+        new Node('11', []),
+        await new Future.value(new Node('12', [])),
+      ]),
+    ]),
+    await new Future.value(new Node('13', [])),
+  ]);
+  String actual = node.toSimpleString();
+  print(actual);
+  if (actual != expected) {
+    throw "Expected '$expected' but got '$actual'";
+  }
+}
+
+class Node {
+  final List<Node>? nested;
+  final String name;
+
+  Node(this.name, [this.nested]) {}
+
+  String toString() => '<$name:[${nested?.join(', ')}]>';
+
+  toSimpleString() {
+    var tmp = nested?.map((child) => child.toSimpleString());
+    return '$name ${tmp?.join(' ')}'.trim();
+  }
+}
diff --git a/tests/language/async_nested/async_nested13_test.dart b/tests/language/async_nested/async_nested13_test.dart
new file mode 100644
index 00000000000..f3fcfe78d41
--- /dev/null
+++ b/tests/language/async_nested/async_nested13_test.dart
@@ -0,0 +1,52 @@
+// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// This has been automatically generated by script
+// "async_nested_test_generator.dart".
+
+import 'dart:async';
+
+void main() async {
+  String expected = "1 2 3 4 5 6 7 8 9 10 11 12 13 14";
+  Node node = new Node('1', [
+    new Node('2', []),
+    await new Future.value(new Node('3', [])),
+    await new Future.value(new Node('4', [
+      new Node('5', [
+        await new Future.value(new Node('6', [
+          new Node('7', [
+            new Node('8', [
+              new Node('9', []),
+              new Node('10', []),
+              await new Future.value(new Node('11', [])),
+            ]),
+            await new Future.value(new Node('12', [])),
+          ]),
+        ])),
+        await new Future.value(new Node('13', [
+          new Node('14', []),
+        ])),
+      ]),
+    ])),
+  ]);
+  String actual = node.toSimpleString();
+  print(actual);
+  if (actual != expected) {
+    throw "Expected '$expected' but got '$actual'";
+  }
+}
+
+class Node {
+  final List<Node>? nested;
+  final String name;
+
+  Node(this.name, [this.nested]) {}
+
+  String toString() => '<$name:[${nested?.join(', ')}]>';
+
+  toSimpleString() {
+    var tmp = nested?.map((child) => child.toSimpleString());
+    return '$name ${tmp?.join(' ')}'.trim();
+  }
+}
diff --git a/tests/language/async_nested/async_nested14_test.dart b/tests/language/async_nested/async_nested14_test.dart
new file mode 100644
index 00000000000..5b8ad8d3ec3
--- /dev/null
+++ b/tests/language/async_nested/async_nested14_test.dart
@@ -0,0 +1,50 @@
+// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// This has been automatically generated by script
+// "async_nested_test_generator.dart".
+
+import 'dart:async';
+
+void main() async {
+  String expected = "1 2 3 4 5 6 7 8 9 10 11 12 13 14";
+  Node node = new Node('1', [
+    new Node('2', []),
+    await new Future.value(new Node('3', [
+      new Node('4', [
+        await new Future.value(new Node('5', [])),
+        new Node('6', []),
+        new Node('7', []),
+        new Node('8', [
+          await new Future.value(new Node('9', [
+            new Node('10', []),
+            await new Future.value(new Node('11', [])),
+          ])),
+        ]),
+        await new Future.value(new Node('12', [])),
+      ]),
+      new Node('13', []),
+    ])),
+    await new Future.value(new Node('14', [])),
+  ]);
+  String actual = node.toSimpleString();
+  print(actual);
+  if (actual != expected) {
+    throw "Expected '$expected' but got '$actual'";
+  }
+}
+
+class Node {
+  final List<Node>? nested;
+  final String name;
+
+  Node(this.name, [this.nested]) {}
+
+  String toString() => '<$name:[${nested?.join(', ')}]>';
+
+  toSimpleString() {
+    var tmp = nested?.map((child) => child.toSimpleString());
+    return '$name ${tmp?.join(' ')}'.trim();
+  }
+}
diff --git a/tests/language/async_nested/async_nested15_test.dart b/tests/language/async_nested/async_nested15_test.dart
new file mode 100644
index 00000000000..3830a53c15c
--- /dev/null
+++ b/tests/language/async_nested/async_nested15_test.dart
@@ -0,0 +1,52 @@
+// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// This has been automatically generated by script
+// "async_nested_test_generator.dart".
+
+import 'dart:async';
+
+void main() async {
+  String expected = "1 2 3 4 5 6 7 8 9 10 11 12 13 14";
+  Node node = new Node('1', [
+    await new Future.value(new Node('2', [
+      await new Future.value(new Node('3', [
+        new Node('4', []),
+        await new Future.value(new Node('5', [
+          await new Future.value(new Node('6', [])),
+          new Node('7', [
+            new Node('8', []),
+            await new Future.value(new Node('9', [])),
+            new Node('10', []),
+            new Node('11', [
+              new Node('12', []),
+            ]),
+          ]),
+        ])),
+        new Node('13', [
+          await new Future.value(new Node('14', [])),
+        ]),
+      ])),
+    ])),
+  ]);
+  String actual = node.toSimpleString();
+  print(actual);
+  if (actual != expected) {
+    throw "Expected '$expected' but got '$actual'";
+  }
+}
+
+class Node {
+  final List<Node>? nested;
+  final String name;
+
+  Node(this.name, [this.nested]) {}
+
+  String toString() => '<$name:[${nested?.join(', ')}]>';
+
+  toSimpleString() {
+    var tmp = nested?.map((child) => child.toSimpleString());
+    return '$name ${tmp?.join(' ')}'.trim();
+  }
+}
diff --git a/tests/language/async_nested/async_nested16_test.dart b/tests/language/async_nested/async_nested16_test.dart
new file mode 100644
index 00000000000..25ad09dbb09
--- /dev/null
+++ b/tests/language/async_nested/async_nested16_test.dart
@@ -0,0 +1,51 @@
+// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// This has been automatically generated by script
+// "async_nested_test_generator.dart".
+
+import 'dart:async';
+
+void main() async {
+  String expected = "1 2 3 4 5 6 7 8 9 10 11 12 13 14";
+  Node node = await new Future.value(new Node('1', [
+    new Node('2', []),
+    await new Future.value(new Node('3', [
+      new Node('4', []),
+      new Node('5', []),
+      new Node('6', []),
+      new Node('7', []),
+      new Node('8', [
+        await new Future.value(new Node('9', [
+          await new Future.value(new Node('10', [])),
+        ])),
+      ]),
+      new Node('11', []),
+    ])),
+    new Node('12', [
+      new Node('13', [
+        await new Future.value(new Node('14', [])),
+      ]),
+    ]),
+  ]));
+  String actual = node.toSimpleString();
+  print(actual);
+  if (actual != expected) {
+    throw "Expected '$expected' but got '$actual'";
+  }
+}
+
+class Node {
+  final List<Node>? nested;
+  final String name;
+
+  Node(this.name, [this.nested]) {}
+
+  String toString() => '<$name:[${nested?.join(', ')}]>';
+
+  toSimpleString() {
+    var tmp = nested?.map((child) => child.toSimpleString());
+    return '$name ${tmp?.join(' ')}'.trim();
+  }
+}
diff --git a/tests/language/async_nested/async_nested17_test.dart b/tests/language/async_nested/async_nested17_test.dart
new file mode 100644
index 00000000000..935121fcb36
--- /dev/null
+++ b/tests/language/async_nested/async_nested17_test.dart
@@ -0,0 +1,49 @@
+// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// This has been automatically generated by script
+// "async_nested_test_generator.dart".
+
+import 'dart:async';
+
+void main() async {
+  String expected = "1 2 3 4 5 6 7 8 9 10 11 12 13 14";
+  Node node = await new Future.value(new Node('1', [
+    new Node('2', []),
+    await new Future.value(new Node('3', [
+      new Node('4', [
+        await new Future.value(new Node('5', [])),
+        new Node('6', []),
+        new Node('7', []),
+      ]),
+      await new Future.value(new Node('8', [])),
+      new Node('9', [
+        new Node('10', []),
+        await new Future.value(new Node('11', [])),
+      ]),
+      await new Future.value(new Node('12', [])),
+    ])),
+    await new Future.value(new Node('13', [])),
+    new Node('14', []),
+  ]));
+  String actual = node.toSimpleString();
+  print(actual);
+  if (actual != expected) {
+    throw "Expected '$expected' but got '$actual'";
+  }
+}
+
+class Node {
+  final List<Node>? nested;
+  final String name;
+
+  Node(this.name, [this.nested]) {}
+
+  String toString() => '<$name:[${nested?.join(', ')}]>';
+
+  toSimpleString() {
+    var tmp = nested?.map((child) => child.toSimpleString());
+    return '$name ${tmp?.join(' ')}'.trim();
+  }
+}
diff --git a/tests/language/async_nested/async_nested18_test.dart b/tests/language/async_nested/async_nested18_test.dart
new file mode 100644
index 00000000000..8377fab4dec
--- /dev/null
+++ b/tests/language/async_nested/async_nested18_test.dart
@@ -0,0 +1,53 @@
+// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// This has been automatically generated by script
+// "async_nested_test_generator.dart".
+
+import 'dart:async';
+
+void main() async {
+  String expected = "1 2 3 4 5 6 7 8 9 10 11 12 13 14 15";
+  Node node = new Node('1', [
+    new Node('2', []),
+    new Node('3', [
+      await new Future.value(new Node('4', [])),
+      new Node('5', [
+        new Node('6', [
+          new Node('7', [
+            await new Future.value(new Node('8', [
+              new Node('9', []),
+              new Node('10', []),
+              await new Future.value(new Node('11', [])),
+              await new Future.value(new Node('12', [])),
+              new Node('13', []),
+            ])),
+            await new Future.value(new Node('14', [
+              new Node('15', []),
+            ])),
+          ]),
+        ]),
+      ]),
+    ]),
+  ]);
+  String actual = node.toSimpleString();
+  print(actual);
+  if (actual != expected) {
+    throw "Expected '$expected' but got '$actual'";
+  }
+}
+
+class Node {
+  final List<Node>? nested;
+  final String name;
+
+  Node(this.name, [this.nested]) {}
+
+  String toString() => '<$name:[${nested?.join(', ')}]>';
+
+  toSimpleString() {
+    var tmp = nested?.map((child) => child.toSimpleString());
+    return '$name ${tmp?.join(' ')}'.trim();
+  }
+}
diff --git a/tests/language/async_nested/async_nested19_test.dart b/tests/language/async_nested/async_nested19_test.dart
new file mode 100644
index 00000000000..18219134fbc
--- /dev/null
+++ b/tests/language/async_nested/async_nested19_test.dart
@@ -0,0 +1,53 @@
+// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// This has been automatically generated by script
+// "async_nested_test_generator.dart".
+
+import 'dart:async';
+
+void main() async {
+  String expected = "1 2 3 4 5 6 7 8 9 10 11 12 13 14 15";
+  Node node = await new Future.value(new Node('1', [
+    new Node('2', []),
+    new Node('3', []),
+    new Node('4', [
+      new Node('5', []),
+    ]),
+    new Node('6', [
+      new Node('7', []),
+    ]),
+    new Node('8', [
+      new Node('9', [
+        await new Future.value(new Node('10', [
+          new Node('11', [
+            new Node('12', []),
+            new Node('13', []),
+            await new Future.value(new Node('14', [])),
+          ]),
+        ])),
+        await new Future.value(new Node('15', [])),
+      ]),
+    ]),
+  ]));
+  String actual = node.toSimpleString();
+  print(actual);
+  if (actual != expected) {
+    throw "Expected '$expected' but got '$actual'";
+  }
+}
+
+class Node {
+  final List<Node>? nested;
+  final String name;
+
+  Node(this.name, [this.nested]) {}
+
+  String toString() => '<$name:[${nested?.join(', ')}]>';
+
+  toSimpleString() {
+    var tmp = nested?.map((child) => child.toSimpleString());
+    return '$name ${tmp?.join(' ')}'.trim();
+  }
+}
diff --git a/tests/language/async_nested/async_nested20_test.dart b/tests/language/async_nested/async_nested20_test.dart
new file mode 100644
index 00000000000..d80f6edeb7b
--- /dev/null
+++ b/tests/language/async_nested/async_nested20_test.dart
@@ -0,0 +1,53 @@
+// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// This has been automatically generated by script
+// "async_nested_test_generator.dart".
+
+import 'dart:async';
+
+void main() async {
+  String expected = "1 2 3 4 5 6 7 8 9 10 11 12 13 14 15";
+  Node node = await new Future.value(new Node('1', [
+    await new Future.value(new Node('2', [
+      new Node('3', []),
+      await new Future.value(new Node('4', [
+        await new Future.value(new Node('5', [
+          new Node('6', []),
+          new Node('7', [
+            await new Future.value(new Node('8', [
+              new Node('9', []),
+            ])),
+            new Node('10', []),
+            new Node('11', []),
+            new Node('12', [
+              await new Future.value(new Node('13', [])),
+              new Node('14', []),
+            ]),
+          ]),
+        ])),
+        await new Future.value(new Node('15', [])),
+      ])),
+    ])),
+  ]));
+  String actual = node.toSimpleString();
+  print(actual);
+  if (actual != expected) {
+    throw "Expected '$expected' but got '$actual'";
+  }
+}
+
+class Node {
+  final List<Node>? nested;
+  final String name;
+
+  Node(this.name, [this.nested]) {}
+
+  String toString() => '<$name:[${nested?.join(', ')}]>';
+
+  toSimpleString() {
+    var tmp = nested?.map((child) => child.toSimpleString());
+    return '$name ${tmp?.join(' ')}'.trim();
+  }
+}
diff --git a/tests/language/async_nested/async_nested21_test.dart b/tests/language/async_nested/async_nested21_test.dart
new file mode 100644
index 00000000000..55210ef7701
--- /dev/null
+++ b/tests/language/async_nested/async_nested21_test.dart
@@ -0,0 +1,54 @@
+// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// This has been automatically generated by script
+// "async_nested_test_generator.dart".
+
+import 'dart:async';
+
+void main() async {
+  String expected = "1 2 3 4 5 6 7 8 9 10 11 12 13 14 15";
+  Node node = await new Future.value(new Node('1', [
+    await new Future.value(new Node('2', [
+      new Node('3', [
+        new Node('4', [
+          await new Future.value(new Node('5', [])),
+          new Node('6', [
+            await new Future.value(new Node('7', [
+              new Node('8', [
+                await new Future.value(new Node('9', [])),
+                new Node('10', []),
+              ]),
+              new Node('11', []),
+              await new Future.value(new Node('12', [])),
+              new Node('13', []),
+            ])),
+            new Node('14', [
+              await new Future.value(new Node('15', [])),
+            ]),
+          ]),
+        ]),
+      ]),
+    ])),
+  ]));
+  String actual = node.toSimpleString();
+  print(actual);
+  if (actual != expected) {
+    throw "Expected '$expected' but got '$actual'";
+  }
+}
+
+class Node {
+  final List<Node>? nested;
+  final String name;
+
+  Node(this.name, [this.nested]) {}
+
+  String toString() => '<$name:[${nested?.join(', ')}]>';
+
+  toSimpleString() {
+    var tmp = nested?.map((child) => child.toSimpleString());
+    return '$name ${tmp?.join(' ')}'.trim();
+  }
+}
diff --git a/tests/language/async_nested/async_nested22_test.dart b/tests/language/async_nested/async_nested22_test.dart
new file mode 100644
index 00000000000..e587a71c503
--- /dev/null
+++ b/tests/language/async_nested/async_nested22_test.dart
@@ -0,0 +1,52 @@
+// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// This has been automatically generated by script
+// "async_nested_test_generator.dart".
+
+import 'dart:async';
+
+void main() async {
+  String expected = "1 2 3 4 5 6 7 8 9 10 11 12 13 14 15";
+  Node node = new Node('1', [
+    await new Future.value(new Node('2', [])),
+    new Node('3', []),
+    await new Future.value(new Node('4', [
+      await new Future.value(new Node('5', [])),
+      new Node('6', [
+        new Node('7', [
+          new Node('8', [
+            new Node('9', []),
+          ]),
+        ]),
+        await new Future.value(new Node('10', [
+          new Node('11', []),
+        ])),
+        await new Future.value(new Node('12', [])),
+      ]),
+      new Node('13', []),
+    ])),
+    await new Future.value(new Node('14', [])),
+    new Node('15', []),
+  ]);
+  String actual = node.toSimpleString();
+  print(actual);
+  if (actual != expected) {
+    throw "Expected '$expected' but got '$actual'";
+  }
+}
+
+class Node {
+  final List<Node>? nested;
+  final String name;
+
+  Node(this.name, [this.nested]) {}
+
+  String toString() => '<$name:[${nested?.join(', ')}]>';
+
+  toSimpleString() {
+    var tmp = nested?.map((child) => child.toSimpleString());
+    return '$name ${tmp?.join(' ')}'.trim();
+  }
+}
diff --git a/tests/language/async_nested/async_nested23_test.dart b/tests/language/async_nested/async_nested23_test.dart
new file mode 100644
index 00000000000..da3b892109b
--- /dev/null
+++ b/tests/language/async_nested/async_nested23_test.dart
@@ -0,0 +1,51 @@
+// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// This has been automatically generated by script
+// "async_nested_test_generator.dart".
+
+import 'dart:async';
+
+void main() async {
+  String expected = "1 2 3 4 5 6 7 8 9 10 11 12 13 14 15";
+  Node node = new Node('1', [
+    await new Future.value(new Node('2', [])),
+    await new Future.value(new Node('3', [
+      new Node('4', [
+        new Node('5', [
+          new Node('6', []),
+          new Node('7', [
+            new Node('8', []),
+          ]),
+          new Node('9', []),
+          await new Future.value(new Node('10', [])),
+          new Node('11', []),
+        ]),
+      ]),
+      new Node('12', []),
+      await new Future.value(new Node('13', [])),
+    ])),
+    await new Future.value(new Node('14', [])),
+    new Node('15', []),
+  ]);
+  String actual = node.toSimpleString();
+  print(actual);
+  if (actual != expected) {
+    throw "Expected '$expected' but got '$actual'";
+  }
+}
+
+class Node {
+  final List<Node>? nested;
+  final String name;
+
+  Node(this.name, [this.nested]) {}
+
+  String toString() => '<$name:[${nested?.join(', ')}]>';
+
+  toSimpleString() {
+    var tmp = nested?.map((child) => child.toSimpleString());
+    return '$name ${tmp?.join(' ')}'.trim();
+  }
+}
diff --git a/tests/language/async_nested/async_nested24_test.dart b/tests/language/async_nested/async_nested24_test.dart
new file mode 100644
index 00000000000..d90e1f9c370
--- /dev/null
+++ b/tests/language/async_nested/async_nested24_test.dart
@@ -0,0 +1,50 @@
+// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// This has been automatically generated by script
+// "async_nested_test_generator.dart".
+
+import 'dart:async';
+
+void main() async {
+  String expected = "1 2 3 4 5 6 7 8 9 10 11 12 13 14 15";
+  Node node = await new Future.value(new Node('1', [
+    new Node('2', []),
+    new Node('3', []),
+    await new Future.value(new Node('4', [
+      await new Future.value(new Node('5', [])),
+      new Node('6', []),
+      await new Future.value(new Node('7', [])),
+      await new Future.value(new Node('8', [])),
+    ])),
+    new Node('9', []),
+    new Node('10', [
+      await new Future.value(new Node('11', [])),
+      new Node('12', [
+        await new Future.value(new Node('13', [])),
+        new Node('14', []),
+        await new Future.value(new Node('15', [])),
+      ]),
+    ]),
+  ]));
+  String actual = node.toSimpleString();
+  print(actual);
+  if (actual != expected) {
+    throw "Expected '$expected' but got '$actual'";
+  }
+}
+
+class Node {
+  final List<Node>? nested;
+  final String name;
+
+  Node(this.name, [this.nested]) {}
+
+  String toString() => '<$name:[${nested?.join(', ')}]>';
+
+  toSimpleString() {
+    var tmp = nested?.map((child) => child.toSimpleString());
+    return '$name ${tmp?.join(' ')}'.trim();
+  }
+}
diff --git a/tests/language/async_nested/async_nested25_test.dart b/tests/language/async_nested/async_nested25_test.dart
new file mode 100644
index 00000000000..db5b481d499
--- /dev/null
+++ b/tests/language/async_nested/async_nested25_test.dart
@@ -0,0 +1,53 @@
+// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// This has been automatically generated by script
+// "async_nested_test_generator.dart".
+
+import 'dart:async';
+
+void main() async {
+  String expected = "1 2 3 4 5 6 7 8 9 10 11 12 13 14 15";
+  Node node = new Node('1', [
+    new Node('2', [
+      new Node('3', [
+        new Node('4', []),
+        await new Future.value(new Node('5', [
+          await new Future.value(new Node('6', [
+            new Node('7', [
+              await new Future.value(new Node('8', [])),
+              new Node('9', []),
+              await new Future.value(new Node('10', [])),
+              await new Future.value(new Node('11', [])),
+              new Node('12', [
+                await new Future.value(new Node('13', [])),
+              ]),
+              new Node('14', []),
+            ]),
+          ])),
+          await new Future.value(new Node('15', [])),
+        ])),
+      ]),
+    ]),
+  ]);
+  String actual = node.toSimpleString();
+  print(actual);
+  if (actual != expected) {
+    throw "Expected '$expected' but got '$actual'";
+  }
+}
+
+class Node {
+  final List<Node>? nested;
+  final String name;
+
+  Node(this.name, [this.nested]) {}
+
+  String toString() => '<$name:[${nested?.join(', ')}]>';
+
+  toSimpleString() {
+    var tmp = nested?.map((child) => child.toSimpleString());
+    return '$name ${tmp?.join(' ')}'.trim();
+  }
+}
diff --git a/tests/language/async_nested/async_nested26_test.dart b/tests/language/async_nested/async_nested26_test.dart
new file mode 100644
index 00000000000..aaf402da030
--- /dev/null
+++ b/tests/language/async_nested/async_nested26_test.dart
@@ -0,0 +1,50 @@
+// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// This has been automatically generated by script
+// "async_nested_test_generator.dart".
+
+import 'dart:async';
+
+void main() async {
+  String expected = "1 2 3 4 5 6 7 8 9 10 11 12 13 14";
+  Node node = new Node('1', [
+    new Node('2', [
+      await new Future.value(new Node('3', [])),
+    ]),
+    await new Future.value(new Node('4', [
+      await new Future.value(new Node('5', [
+        new Node('6', [
+          new Node('7', []),
+        ]),
+        new Node('8', []),
+        await new Future.value(new Node('9', [])),
+        new Node('10', []),
+        new Node('11', []),
+      ])),
+      await new Future.value(new Node('12', [])),
+      new Node('13', []),
+      new Node('14', []),
+    ])),
+  ]);
+  String actual = node.toSimpleString();
+  print(actual);
+  if (actual != expected) {
+    throw "Expected '$expected' but got '$actual'";
+  }
+}
+
+class Node {
+  final List<Node>? nested;
+  final String name;
+
+  Node(this.name, [this.nested]) {}
+
+  String toString() => '<$name:[${nested?.join(', ')}]>';
+
+  toSimpleString() {
+    var tmp = nested?.map((child) => child.toSimpleString());
+    return '$name ${tmp?.join(' ')}'.trim();
+  }
+}
diff --git a/tests/language/async_nested/async_nested27_test.dart b/tests/language/async_nested/async_nested27_test.dart
new file mode 100644
index 00000000000..f2e59cf2428
--- /dev/null
+++ b/tests/language/async_nested/async_nested27_test.dart
@@ -0,0 +1,53 @@
+// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// This has been automatically generated by script
+// "async_nested_test_generator.dart".
+
+import 'dart:async';
+
+void main() async {
+  String expected = "1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16";
+  Node node = new Node('1', [
+    new Node('2', []),
+    await new Future.value(new Node('3', [
+      new Node('4', []),
+      await new Future.value(new Node('5', [
+        new Node('6', []),
+        await new Future.value(new Node('7', [
+          new Node('8', []),
+        ])),
+      ])),
+    ])),
+    await new Future.value(new Node('9', [
+      new Node('10', [
+        new Node('11', []),
+        new Node('12', []),
+        await new Future.value(new Node('13', [])),
+        await new Future.value(new Node('14', [])),
+        await new Future.value(new Node('15', [])),
+        new Node('16', []),
+      ]),
+    ])),
+  ]);
+  String actual = node.toSimpleString();
+  print(actual);
+  if (actual != expected) {
+    throw "Expected '$expected' but got '$actual'";
+  }
+}
+
+class Node {
+  final List<Node>? nested;
+  final String name;
+
+  Node(this.name, [this.nested]) {}
+
+  String toString() => '<$name:[${nested?.join(', ')}]>';
+
+  toSimpleString() {
+    var tmp = nested?.map((child) => child.toSimpleString());
+    return '$name ${tmp?.join(' ')}'.trim();
+  }
+}
diff --git a/tests/language/async_nested/async_nested28_test.dart b/tests/language/async_nested/async_nested28_test.dart
new file mode 100644
index 00000000000..8f94d8b2e51
--- /dev/null
+++ b/tests/language/async_nested/async_nested28_test.dart
@@ -0,0 +1,54 @@
+// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// This has been automatically generated by script
+// "async_nested_test_generator.dart".
+
+import 'dart:async';
+
+void main() async {
+  String expected = "1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16";
+  Node node = new Node('1', [
+    await new Future.value(new Node('2', [
+      new Node('3', []),
+      new Node('4', []),
+      new Node('5', [
+        new Node('6', []),
+        await new Future.value(new Node('7', [
+          new Node('8', [
+            new Node('9', []),
+            new Node('10', [
+              new Node('11', [
+                new Node('12', []),
+                new Node('13', []),
+                await new Future.value(new Node('14', [])),
+              ]),
+            ]),
+          ]),
+        ])),
+        new Node('15', []),
+        await new Future.value(new Node('16', [])),
+      ]),
+    ])),
+  ]);
+  String actual = node.toSimpleString();
+  print(actual);
+  if (actual != expected) {
+    throw "Expected '$expected' but got '$actual'";
+  }
+}
+
+class Node {
+  final List<Node>? nested;
+  final String name;
+
+  Node(this.name, [this.nested]) {}
+
+  String toString() => '<$name:[${nested?.join(', ')}]>';
+
+  toSimpleString() {
+    var tmp = nested?.map((child) => child.toSimpleString());
+    return '$name ${tmp?.join(' ')}'.trim();
+  }
+}
diff --git a/tests/language/async_nested/async_nested29_test.dart b/tests/language/async_nested/async_nested29_test.dart
new file mode 100644
index 00000000000..aa2bc6f8550
--- /dev/null
+++ b/tests/language/async_nested/async_nested29_test.dart
@@ -0,0 +1,55 @@
+// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// This has been automatically generated by script
+// "async_nested_test_generator.dart".
+
+import 'dart:async';
+
+void main() async {
+  String expected = "1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16";
+  Node node = new Node('1', [
+    await new Future.value(new Node('2', [
+      new Node('3', []),
+      await new Future.value(new Node('4', [])),
+      new Node('5', [
+        new Node('6', []),
+        await new Future.value(new Node('7', [
+          new Node('8', [
+            await new Future.value(new Node('9', [])),
+            await new Future.value(new Node('10', [
+              new Node('11', [
+                new Node('12', [
+                  await new Future.value(new Node('13', [])),
+                ]),
+                new Node('14', []),
+                await new Future.value(new Node('15', [])),
+              ]),
+            ])),
+            await new Future.value(new Node('16', [])),
+          ]),
+        ])),
+      ]),
+    ])),
+  ]);
+  String actual = node.toSimpleString();
+  print(actual);
+  if (actual != expected) {
+    throw "Expected '$expected' but got '$actual'";
+  }
+}
+
+class Node {
+  final List<Node>? nested;
+  final String name;
+
+  Node(this.name, [this.nested]) {}
+
+  String toString() => '<$name:[${nested?.join(', ')}]>';
+
+  toSimpleString() {
+    var tmp = nested?.map((child) => child.toSimpleString());
+    return '$name ${tmp?.join(' ')}'.trim();
+  }
+}
diff --git a/tests/language/async_nested/async_nested30_test.dart b/tests/language/async_nested/async_nested30_test.dart
new file mode 100644
index 00000000000..d43e9c0a6d6
--- /dev/null
+++ b/tests/language/async_nested/async_nested30_test.dart
@@ -0,0 +1,54 @@
+// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// This has been automatically generated by script
+// "async_nested_test_generator.dart".
+
+import 'dart:async';
+
+void main() async {
+  String expected = "1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16";
+  Node node = new Node('1', [
+    new Node('2', [
+      new Node('3', []),
+      new Node('4', []),
+      new Node('5', [
+        await new Future.value(new Node('6', [
+          new Node('7', []),
+          new Node('8', [
+            await new Future.value(new Node('9', [])),
+            await new Future.value(new Node('10', [])),
+            await new Future.value(new Node('11', [])),
+          ]),
+          await new Future.value(new Node('12', [])),
+          new Node('13', []),
+        ])),
+        new Node('14', [
+          await new Future.value(new Node('15', [
+            new Node('16', []),
+          ])),
+        ]),
+      ]),
+    ]),
+  ]);
+  String actual = node.toSimpleString();
+  print(actual);
+  if (actual != expected) {
+    throw "Expected '$expected' but got '$actual'";
+  }
+}
+
+class Node {
+  final List<Node>? nested;
+  final String name;
+
+  Node(this.name, [this.nested]) {}
+
+  String toString() => '<$name:[${nested?.join(', ')}]>';
+
+  toSimpleString() {
+    var tmp = nested?.map((child) => child.toSimpleString());
+    return '$name ${tmp?.join(' ')}'.trim();
+  }
+}
diff --git a/tests/language/async_nested/async_nested31_test.dart b/tests/language/async_nested/async_nested31_test.dart
new file mode 100644
index 00000000000..833b62f119c
--- /dev/null
+++ b/tests/language/async_nested/async_nested31_test.dart
@@ -0,0 +1,53 @@
+// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// This has been automatically generated by script
+// "async_nested_test_generator.dart".
+
+import 'dart:async';
+
+void main() async {
+  String expected = "1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16";
+  Node node = new Node('1', [
+    await new Future.value(new Node('2', [])),
+    await new Future.value(new Node('3', [
+      new Node('4', [
+        new Node('5', []),
+        new Node('6', []),
+        await new Future.value(new Node('7', [])),
+        await new Future.value(new Node('8', [
+          new Node('9', []),
+        ])),
+        new Node('10', [
+          new Node('11', [
+            new Node('12', []),
+          ]),
+        ]),
+      ]),
+    ])),
+    await new Future.value(new Node('13', [])),
+    await new Future.value(new Node('14', [])),
+    new Node('15', []),
+    await new Future.value(new Node('16', [])),
+  ]);
+  String actual = node.toSimpleString();
+  print(actual);
+  if (actual != expected) {
+    throw "Expected '$expected' but got '$actual'";
+  }
+}
+
+class Node {
+  final List<Node>? nested;
+  final String name;
+
+  Node(this.name, [this.nested]) {}
+
+  String toString() => '<$name:[${nested?.join(', ')}]>';
+
+  toSimpleString() {
+    var tmp = nested?.map((child) => child.toSimpleString());
+    return '$name ${tmp?.join(' ')}'.trim();
+  }
+}
diff --git a/tests/language/async_nested/async_nested32_test.dart b/tests/language/async_nested/async_nested32_test.dart
new file mode 100644
index 00000000000..fcec85ee662
--- /dev/null
+++ b/tests/language/async_nested/async_nested32_test.dart
@@ -0,0 +1,54 @@
+// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// This has been automatically generated by script
+// "async_nested_test_generator.dart".
+
+import 'dart:async';
+
+void main() async {
+  String expected = "1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16";
+  Node node = new Node('1', [
+    new Node('2', [
+      new Node('3', []),
+      new Node('4', []),
+      await new Future.value(new Node('5', [
+        await new Future.value(new Node('6', [
+          await new Future.value(new Node('7', [])),
+          new Node('8', [
+            new Node('9', []),
+            await new Future.value(new Node('10', [])),
+          ]),
+        ])),
+      ])),
+      await new Future.value(new Node('11', [])),
+      new Node('12', [
+        new Node('13', []),
+        await new Future.value(new Node('14', [
+          await new Future.value(new Node('15', [])),
+        ])),
+        new Node('16', []),
+      ]),
+    ]),
+  ]);
+  String actual = node.toSimpleString();
+  print(actual);
+  if (actual != expected) {
+    throw "Expected '$expected' but got '$actual'";
+  }
+}
+
+class Node {
+  final List<Node>? nested;
+  final String name;
+
+  Node(this.name, [this.nested]) {}
+
+  String toString() => '<$name:[${nested?.join(', ')}]>';
+
+  toSimpleString() {
+    var tmp = nested?.map((child) => child.toSimpleString());
+    return '$name ${tmp?.join(' ')}'.trim();
+  }
+}
diff --git a/tests/language/async_nested/async_nested33_test.dart b/tests/language/async_nested/async_nested33_test.dart
new file mode 100644
index 00000000000..b72943aace2
--- /dev/null
+++ b/tests/language/async_nested/async_nested33_test.dart
@@ -0,0 +1,55 @@
+// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// This has been automatically generated by script
+// "async_nested_test_generator.dart".
+
+import 'dart:async';
+
+void main() async {
+  String expected = "1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16";
+  Node node = new Node('1', [
+    new Node('2', []),
+    new Node('3', [
+      await new Future.value(new Node('4', [])),
+      new Node('5', [
+        new Node('6', [
+          new Node('7', [
+            await new Future.value(new Node('8', [])),
+            await new Future.value(new Node('9', [
+              await new Future.value(new Node('10', [
+                new Node('11', []),
+              ])),
+              await new Future.value(new Node('12', [])),
+              await new Future.value(new Node('13', [
+                await new Future.value(new Node('14', [])),
+              ])),
+            ])),
+            await new Future.value(new Node('15', [])),
+            new Node('16', []),
+          ]),
+        ]),
+      ]),
+    ]),
+  ]);
+  String actual = node.toSimpleString();
+  print(actual);
+  if (actual != expected) {
+    throw "Expected '$expected' but got '$actual'";
+  }
+}
+
+class Node {
+  final List<Node>? nested;
+  final String name;
+
+  Node(this.name, [this.nested]) {}
+
+  String toString() => '<$name:[${nested?.join(', ')}]>';
+
+  toSimpleString() {
+    var tmp = nested?.map((child) => child.toSimpleString());
+    return '$name ${tmp?.join(' ')}'.trim();
+  }
+}
diff --git a/tests/language/async_nested/async_nested34_test.dart b/tests/language/async_nested/async_nested34_test.dart
new file mode 100644
index 00000000000..d13eb14fc5c
--- /dev/null
+++ b/tests/language/async_nested/async_nested34_test.dart
@@ -0,0 +1,54 @@
+// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// This has been automatically generated by script
+// "async_nested_test_generator.dart".
+
+import 'dart:async';
+
+void main() async {
+  String expected = "1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16";
+  Node node = await new Future.value(new Node('1', [
+    await new Future.value(new Node('2', [
+      new Node('3', []),
+      new Node('4', []),
+      new Node('5', [
+        await new Future.value(new Node('6', [
+          new Node('7', [
+            new Node('8', []),
+            new Node('9', [
+              new Node('10', []),
+              await new Future.value(new Node('11', [])),
+            ]),
+          ]),
+          await new Future.value(new Node('12', [])),
+        ])),
+        new Node('13', [
+          await new Future.value(new Node('14', [])),
+          await new Future.value(new Node('15', [])),
+          new Node('16', []),
+        ]),
+      ]),
+    ])),
+  ]));
+  String actual = node.toSimpleString();
+  print(actual);
+  if (actual != expected) {
+    throw "Expected '$expected' but got '$actual'";
+  }
+}
+
+class Node {
+  final List<Node>? nested;
+  final String name;
+
+  Node(this.name, [this.nested]) {}
+
+  String toString() => '<$name:[${nested?.join(', ')}]>';
+
+  toSimpleString() {
+    var tmp = nested?.map((child) => child.toSimpleString());
+    return '$name ${tmp?.join(' ')}'.trim();
+  }
+}
diff --git a/tests/language/async_nested/async_nested35_test.dart b/tests/language/async_nested/async_nested35_test.dart
new file mode 100644
index 00000000000..07c06a2bd94
--- /dev/null
+++ b/tests/language/async_nested/async_nested35_test.dart
@@ -0,0 +1,54 @@
+// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// This has been automatically generated by script
+// "async_nested_test_generator.dart".
+
+import 'dart:async';
+
+void main() async {
+  String expected = "1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16";
+  Node node = await new Future.value(new Node('1', [
+    new Node('2', []),
+    await new Future.value(new Node('3', [
+      await new Future.value(new Node('4', [])),
+      await new Future.value(new Node('5', [
+        new Node('6', []),
+        new Node('7', []),
+        await new Future.value(new Node('8', [])),
+        await new Future.value(new Node('9', [])),
+      ])),
+      new Node('10', [
+        new Node('11', [
+          new Node('12', [
+            new Node('13', []),
+          ]),
+        ]),
+        new Node('14', [
+          await new Future.value(new Node('15', [])),
+        ]),
+        new Node('16', []),
+      ]),
+    ])),
+  ]));
+  String actual = node.toSimpleString();
+  print(actual);
+  if (actual != expected) {
+    throw "Expected '$expected' but got '$actual'";
+  }
+}
+
+class Node {
+  final List<Node>? nested;
+  final String name;
+
+  Node(this.name, [this.nested]) {}
+
+  String toString() => '<$name:[${nested?.join(', ')}]>';
+
+  toSimpleString() {
+    var tmp = nested?.map((child) => child.toSimpleString());
+    return '$name ${tmp?.join(' ')}'.trim();
+  }
+}
diff --git a/tests/language/async_nested/async_nested36_test.dart b/tests/language/async_nested/async_nested36_test.dart
new file mode 100644
index 00000000000..92a320fbac0
--- /dev/null
+++ b/tests/language/async_nested/async_nested36_test.dart
@@ -0,0 +1,52 @@
+// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// This has been automatically generated by script
+// "async_nested_test_generator.dart".
+
+import 'dart:async';
+
+void main() async {
+  String expected = "1 2 3 4 5 6 7 8 9 10 11 12 13 14 15";
+  Node node = await new Future.value(new Node('1', [
+    await new Future.value(new Node('2', [
+      await new Future.value(new Node('3', [])),
+      new Node('4', []),
+      await new Future.value(new Node('5', [
+        new Node('6', [
+          new Node('7', []),
+          await new Future.value(new Node('8', [])),
+        ]),
+        new Node('9', []),
+        await new Future.value(new Node('10', [])),
+      ])),
+      new Node('11', [
+        new Node('12', []),
+      ]),
+      new Node('13', [
+        await new Future.value(new Node('14', [])),
+      ]),
+    ])),
+    await new Future.value(new Node('15', [])),
+  ]));
+  String actual = node.toSimpleString();
+  print(actual);
+  if (actual != expected) {
+    throw "Expected '$expected' but got '$actual'";
+  }
+}
+
+class Node {
+  final List<Node>? nested;
+  final String name;
+
+  Node(this.name, [this.nested]) {}
+
+  String toString() => '<$name:[${nested?.join(', ')}]>';
+
+  toSimpleString() {
+    var tmp = nested?.map((child) => child.toSimpleString());
+    return '$name ${tmp?.join(' ')}'.trim();
+  }
+}
diff --git a/tests/language/async_nested/async_nested37_test.dart b/tests/language/async_nested/async_nested37_test.dart
new file mode 100644
index 00000000000..3c0a33eb0a8
--- /dev/null
+++ b/tests/language/async_nested/async_nested37_test.dart
@@ -0,0 +1,53 @@
+// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// This has been automatically generated by script
+// "async_nested_test_generator.dart".
+
+import 'dart:async';
+
+void main() async {
+  String expected = "1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16";
+  Node node = new Node('1', [
+    new Node('2', []),
+    await new Future.value(new Node('3', [])),
+    new Node('4', [
+      new Node('5', [
+        new Node('6', []),
+        new Node('7', []),
+      ]),
+    ]),
+    await new Future.value(new Node('8', [
+      await new Future.value(new Node('9', [])),
+      await new Future.value(new Node('10', [
+        new Node('11', []),
+        new Node('12', []),
+        await new Future.value(new Node('13', [])),
+      ])),
+    ])),
+    await new Future.value(new Node('14', [])),
+    new Node('15', [
+      new Node('16', []),
+    ]),
+  ]);
+  String actual = node.toSimpleString();
+  print(actual);
+  if (actual != expected) {
+    throw "Expected '$expected' but got '$actual'";
+  }
+}
+
+class Node {
+  final List<Node>? nested;
+  final String name;
+
+  Node(this.name, [this.nested]) {}
+
+  String toString() => '<$name:[${nested?.join(', ')}]>';
+
+  toSimpleString() {
+    var tmp = nested?.map((child) => child.toSimpleString());
+    return '$name ${tmp?.join(' ')}'.trim();
+  }
+}
diff --git a/tests/language/async_nested/async_nested38_test.dart b/tests/language/async_nested/async_nested38_test.dart
new file mode 100644
index 00000000000..c74c7631990
--- /dev/null
+++ b/tests/language/async_nested/async_nested38_test.dart
@@ -0,0 +1,52 @@
+// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// This has been automatically generated by script
+// "async_nested_test_generator.dart".
+
+import 'dart:async';
+
+void main() async {
+  String expected = "1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16";
+  Node node = await new Future.value(new Node('1', [
+    new Node('2', []),
+    new Node('3', [
+      new Node('4', []),
+    ]),
+    new Node('5', []),
+    new Node('6', []),
+    await new Future.value(new Node('7', [])),
+    await new Future.value(new Node('8', [
+      await new Future.value(new Node('9', [])),
+      new Node('10', [
+        new Node('11', []),
+        await new Future.value(new Node('12', [])),
+      ]),
+    ])),
+    new Node('13', [
+      new Node('14', []),
+    ]),
+    await new Future.value(new Node('15', [])),
+    await new Future.value(new Node('16', [])),
+  ]));
+  String actual = node.toSimpleString();
+  print(actual);
+  if (actual != expected) {
+    throw "Expected '$expected' but got '$actual'";
+  }
+}
+
+class Node {
+  final List<Node>? nested;
+  final String name;
+
+  Node(this.name, [this.nested]) {}
+
+  String toString() => '<$name:[${nested?.join(', ')}]>';
+
+  toSimpleString() {
+    var tmp = nested?.map((child) => child.toSimpleString());
+    return '$name ${tmp?.join(' ')}'.trim();
+  }
+}
diff --git a/tests/language/async_nested/async_nested39_test.dart b/tests/language/async_nested/async_nested39_test.dart
new file mode 100644
index 00000000000..833453a0a8a
--- /dev/null
+++ b/tests/language/async_nested/async_nested39_test.dart
@@ -0,0 +1,43 @@
+// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// This has been automatically generated by script
+// "async_nested_test_generator.dart".
+
+import 'dart:async';
+
+void main() async {
+  String expected = "1 2 3 4 5 6 7 8 9";
+  Node node = await new Future.value(new Node('1', [
+    new Node('2', []),
+    await new Future.value(new Node('3', [
+      new Node('4', []),
+      new Node('5', []),
+      await new Future.value(new Node('6', [
+        new Node('7', []),
+      ])),
+    ])),
+    new Node('8', []),
+    await new Future.value(new Node('9', [])),
+  ]));
+  String actual = node.toSimpleString();
+  print(actual);
+  if (actual != expected) {
+    throw "Expected '$expected' but got '$actual'";
+  }
+}
+
+class Node {
+  final List<Node>? nested;
+  final String name;
+
+  Node(this.name, [this.nested]) {}
+
+  String toString() => '<$name:[${nested?.join(', ')}]>';
+
+  toSimpleString() {
+    var tmp = nested?.map((child) => child.toSimpleString());
+    return '$name ${tmp?.join(' ')}'.trim();
+  }
+}
diff --git a/tests/language/async_nested/async_nested40_test.dart b/tests/language/async_nested/async_nested40_test.dart
new file mode 100644
index 00000000000..b049362153f
--- /dev/null
+++ b/tests/language/async_nested/async_nested40_test.dart
@@ -0,0 +1,44 @@
+// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// This has been automatically generated by script
+// "async_nested_test_generator.dart".
+
+import 'dart:async';
+
+void main() async {
+  String expected = "1 2 3 4 5 6 7 8 9";
+  Node node = await new Future.value(new Node('1', [
+    new Node('2', [
+      new Node('3', [
+        new Node('4', []),
+      ]),
+    ]),
+    await new Future.value(new Node('5', [
+      new Node('6', []),
+      new Node('7', []),
+      await new Future.value(new Node('8', [])),
+    ])),
+    await new Future.value(new Node('9', [])),
+  ]));
+  String actual = node.toSimpleString();
+  print(actual);
+  if (actual != expected) {
+    throw "Expected '$expected' but got '$actual'";
+  }
+}
+
+class Node {
+  final List<Node>? nested;
+  final String name;
+
+  Node(this.name, [this.nested]) {}
+
+  String toString() => '<$name:[${nested?.join(', ')}]>';
+
+  toSimpleString() {
+    var tmp = nested?.map((child) => child.toSimpleString());
+    return '$name ${tmp?.join(' ')}'.trim();
+  }
+}
diff --git a/tests/language/async_nested/async_nested41_test.dart b/tests/language/async_nested/async_nested41_test.dart
new file mode 100644
index 00000000000..a3816afea2a
--- /dev/null
+++ b/tests/language/async_nested/async_nested41_test.dart
@@ -0,0 +1,43 @@
+// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// This has been automatically generated by script
+// "async_nested_test_generator.dart".
+
+import 'dart:async';
+
+void main() async {
+  String expected = "1 2 3 4 5 6 7 8 9";
+  Node node = new Node('1', [
+    await new Future.value(new Node('2', [])),
+    await new Future.value(new Node('3', [
+      new Node('4', []),
+      await new Future.value(new Node('5', [
+        new Node('6', []),
+      ])),
+      await new Future.value(new Node('7', [])),
+      new Node('8', []),
+    ])),
+    await new Future.value(new Node('9', [])),
+  ]);
+  String actual = node.toSimpleString();
+  print(actual);
+  if (actual != expected) {
+    throw "Expected '$expected' but got '$actual'";
+  }
+}
+
+class Node {
+  final List<Node>? nested;
+  final String name;
+
+  Node(this.name, [this.nested]) {}
+
+  String toString() => '<$name:[${nested?.join(', ')}]>';
+
+  toSimpleString() {
+    var tmp = nested?.map((child) => child.toSimpleString());
+    return '$name ${tmp?.join(' ')}'.trim();
+  }
+}
diff --git a/tools/test_generators/async_nested_test_generator.dart b/tools/test_generators/async_nested_test_generator.dart
index 2d09a390fea..658e917b39b 100644
--- a/tools/test_generators/async_nested_test_generator.dart
+++ b/tools/test_generators/async_nested_test_generator.dart
@@ -117,7 +117,7 @@ void main() async {
 }
 
 class Node {
-  final List<Node> nested;
+  final List<Node>? nested;
   final String name;
 
   Node(this.name, [this.nested]) {