diff --git a/LanguageFeatures/Augmentation-libraries/augmented_expression_A09_t14.dart b/LanguageFeatures/Augmentation-libraries/augmented_expression_A09_t14.dart
new file mode 100644
index 0000000000..8e7a860490
--- /dev/null
+++ b/LanguageFeatures/Augmentation-libraries/augmented_expression_A09_t14.dart
@@ -0,0 +1,24 @@
+// Copyright (c) 2024, 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.
+
+/// @assertion A compile-time error occurs if a declaration with the basename
+/// `augmented` occurs in a location where any enclosing declaration is
+/// augmenting.
+///
+/// @description Checks that it is a compile-time error to augment a class named
+/// `augmented`.
+/// @author sgrekhov22@gmail.com
+
+// SharedOptions=--enable-experiment=macros
+
+class augmented {}
+
+augment class augmented {}
+//            ^^^^^^^^^
+// [analyzer] unspecified
+// [cfe] unspecified
+
+main() {
+  print(augmented);
+}
diff --git a/LanguageFeatures/Augmentation-libraries/augmented_expression_A09_t15.dart b/LanguageFeatures/Augmentation-libraries/augmented_expression_A09_t15.dart
new file mode 100644
index 0000000000..042b8365ac
--- /dev/null
+++ b/LanguageFeatures/Augmentation-libraries/augmented_expression_A09_t15.dart
@@ -0,0 +1,24 @@
+// Copyright (c) 2024, 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.
+
+/// @assertion A compile-time error occurs if a declaration with the basename
+/// `augmented` occurs in a location where any enclosing declaration is
+/// augmenting.
+///
+/// @description Checks that it is a compile-time error to augment a mixin named
+/// `augmented`.
+/// @author sgrekhov22@gmail.com
+
+// SharedOptions=--enable-experiment=macros
+
+mixin augmented {}
+
+augment mixin augmented {}
+//            ^^^^^^^^^
+// [analyzer] unspecified
+// [cfe] unspecified
+
+main() {
+  print(augmented);
+}
diff --git a/LanguageFeatures/Augmentation-libraries/augmented_expression_A09_t16.dart b/LanguageFeatures/Augmentation-libraries/augmented_expression_A09_t16.dart
new file mode 100644
index 0000000000..fc6b2ddc11
--- /dev/null
+++ b/LanguageFeatures/Augmentation-libraries/augmented_expression_A09_t16.dart
@@ -0,0 +1,28 @@
+// Copyright (c) 2024, 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.
+
+/// @assertion A compile-time error occurs if a declaration with the basename
+/// `augmented` occurs in a location where any enclosing declaration is
+/// augmenting.
+///
+/// @description Checks that it is a compile-time error to augment an enum named
+/// `augmented`.
+/// @author sgrekhov22@gmail.com
+
+// SharedOptions=--enable-experiment=macros
+
+enum augmented {
+  e0;
+}
+
+augment enum augmented {
+//           ^^^^^^^^^
+// [analyzer] unspecified
+// [cfe] unspecified
+  e1;
+}
+
+main() {
+  print(augmented);
+}
diff --git a/LanguageFeatures/Augmentation-libraries/augmented_expression_A09_t17.dart b/LanguageFeatures/Augmentation-libraries/augmented_expression_A09_t17.dart
new file mode 100644
index 0000000000..5077c8642c
--- /dev/null
+++ b/LanguageFeatures/Augmentation-libraries/augmented_expression_A09_t17.dart
@@ -0,0 +1,26 @@
+// Copyright (c) 2024, 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.
+
+/// @assertion A compile-time error occurs if a declaration with the basename
+/// `augmented` occurs in a location where any enclosing declaration is
+/// augmenting.
+///
+/// @description Checks that it is a compile-time error to augment an extension
+/// named `augmented`.
+/// @author sgrekhov22@gmail.com
+
+// SharedOptions=--enable-experiment=macros
+
+class A {}
+
+extension augmented on A {}
+
+augment extension augmented {}
+//                ^^^^^^^^^
+// [analyzer] unspecified
+// [cfe] unspecified
+
+main() {
+  print(A);
+}
diff --git a/LanguageFeatures/Augmentation-libraries/augmented_expression_A09_t18.dart b/LanguageFeatures/Augmentation-libraries/augmented_expression_A09_t18.dart
new file mode 100644
index 0000000000..8bcd589aa7
--- /dev/null
+++ b/LanguageFeatures/Augmentation-libraries/augmented_expression_A09_t18.dart
@@ -0,0 +1,24 @@
+// Copyright (c) 2024, 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.
+
+/// @assertion A compile-time error occurs if a declaration with the basename
+/// `augmented` occurs in a location where any enclosing declaration is
+/// augmenting.
+///
+/// @description Checks that it is a compile-time error to augment an extension
+/// type named `augmented`.
+/// @author sgrekhov22@gmail.com
+
+// SharedOptions=--enable-experiment=macros
+
+extension type augmented(int _) {}
+
+augment extension type augmented {}
+//                     ^^^^^^^^^
+// [analyzer] unspecified
+// [cfe] unspecified
+
+main() {
+  print(augmented);
+}
diff --git a/LanguageFeatures/Augmentation-libraries/augmented_expression_A11_t28.dart b/LanguageFeatures/Augmentation-libraries/augmented_expression_A11_t28.dart
new file mode 100644
index 0000000000..41d92cf510
--- /dev/null
+++ b/LanguageFeatures/Augmentation-libraries/augmented_expression_A11_t28.dart
@@ -0,0 +1,61 @@
+// Copyright (c) 2024, 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.
+
+/// @assertion The exact result of an `augmented` expression depends on what is
+/// being augmented, but it generally follows the same rules as any normal
+/// identifier:
+/// ...
+/// - Augmenting non-redirecting generative constructors: Unlike other
+///   functions, `augmented` has no special meaning in non-redirecting
+///   generative constructors. It is still a reserved word inside the body of
+///   these constructors, since they are within the scope of an augmenting
+///   declaration.
+///
+/// @description Checks that it is a compile-time error for an augmenting
+/// non-redirecting generative constructor to initialize a member named
+/// `augmented` in the initializer list.
+/// @author sgrekhov22@gmail.com
+
+// SharedOptions=--enable-experiment=macros
+
+class C {
+  int augmented;
+  C(this.augmented);
+}
+
+augment class C {
+  C.foo() : augmented = 1;
+//          ^^^^^^^^^
+// [analyzer] unspecified
+// [cfe] unspecified
+}
+
+enum E {
+  a0(0);
+  final int augmented;
+  const E(this.augmented);
+}
+
+augment enum E {
+  a1.foo();
+  const E.foo() : augmented = 1;
+//                ^^^^^^^^^
+// [analyzer] unspecified
+// [cfe] unspecified
+}
+
+extension type ET(int augmented) {}
+
+augment extension type ET {
+  ET.foo() : augmented = 1 {}
+//           ^^^^^^^^^
+// [analyzer] unspecified
+// [cfe] unspecified
+}
+
+main() {
+  print(C);
+  print(E);
+  print(ET);
+}
diff --git a/LanguageFeatures/Augmentation-libraries/augmented_expression_A11_t29.dart b/LanguageFeatures/Augmentation-libraries/augmented_expression_A11_t29.dart
new file mode 100644
index 0000000000..5528bd56a7
--- /dev/null
+++ b/LanguageFeatures/Augmentation-libraries/augmented_expression_A11_t29.dart
@@ -0,0 +1,63 @@
+// Copyright (c) 2024, 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.
+
+/// @assertion The exact result of an `augmented` expression depends on what is
+/// being augmented, but it generally follows the same rules as any normal
+/// identifier:
+/// ...
+/// - Augmenting non-redirecting generative constructors: Unlike other
+///   functions, `augmented` has no special meaning in non-redirecting
+///   generative constructors. It is still a reserved word inside the body of
+///   these constructors, since they are within the scope of an augmenting
+///   declaration.
+///
+/// @description Checks that it is a compile-time error for an augmenting
+/// non-redirecting generative constructor to use a variable named `augmented`
+/// in the initializer list.
+/// @author sgrekhov22@gmail.com
+
+// SharedOptions=--enable-experiment=macros
+
+const augmented = 1;
+
+class C {
+  int id;
+  C(this.id);
+}
+
+augment class C {
+  C.foo() : id = augmented;
+//               ^^^^^^^^^
+// [analyzer] unspecified
+// [cfe] unspecified
+}
+
+enum E {
+  a0(0);
+  final int id;
+  const E(this.id);
+}
+
+augment enum E {
+  a1.foo();
+  const E.foo() : id = augmented;
+//                     ^^^^^^^^^
+// [analyzer] unspecified
+// [cfe] unspecified
+}
+
+extension type ET(int id) {}
+
+augment extension type ET {
+  ET.foo() : id = augmented;
+//                ^^^^^^^^^
+// [analyzer] unspecified
+// [cfe] unspecified
+}
+
+main() {
+  print(C);
+  print(E);
+  print(ET);
+}
diff --git a/LanguageFeatures/Augmentation-libraries/extension_types_A02_t06.dart b/LanguageFeatures/Augmentation-libraries/extension_types_A02_t06.dart
index bbd56bafbd..3335894855 100644
--- a/LanguageFeatures/Augmentation-libraries/extension_types_A02_t06.dart
+++ b/LanguageFeatures/Augmentation-libraries/extension_types_A02_t06.dart
@@ -19,4 +19,9 @@ extension type ET(int id) {}
 
 main() {
   Expect.equals(1, ET(1).id);
+  if (assertStatementsEnabled) {
+    Expect.throws(() {
+      ET(-1);
+    });
+  }
 }