#993. NativeFunction test added

LibTest/ffi/NativeFunction/NativeFunction_A01_t01.dart

@@ -0,0 +1,37 @@
+// Copyright (c) 2021, 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 Represents a function type in C.
+///
+/// NativeFunction is not constructible in the Dart code and serves purely as
+/// marker in type signatures.
+///
+/// @description Checks that this class cannot be extended
+/// @author sgrekhov@unipro.ru
+
+import "dart:ffi";
+
+class C1<T extends Function> extends NativeFunction<T> {
+//                                   ^^^^^^^^^^^^^^
+// [analyzer] unspecified
+// [cfe] unspecified
+}
+
+class C2<T extends Function> implements NativeFunction<T> {
+//                                      ^^^^^^^^^^^^^^^^^
+// [analyzer] unspecified
+// [cfe] unspecified
+}
+
+class C3 extends Object with NativeFunction {
+//                           ^^^^^^^^^^^^^^
+// [analyzer] unspecified
+// [cfe] unspecified
+}
+
+void main() {
+  C1? c1;
+  C2? c2;
+  C3? c3;
+}