Add async function test

test/language/statements/class/subclass/superclass-async-function.js

@@ -0,0 +1,51 @@
+// Copyright (C) 2020 Alexey Shvayka. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-runtime-semantics-classdefinitionevaluation
+description: >
+  IsConstructor check is performed before "prototype" lookup.
+  Async functions are not constructors (MakeConstructor is not called on them).
+info: |
+  ClassDefinitionEvaluation
+
+  [...]
+  5. Else,
+    [...]
+    d. Let superclass be ? GetValue(superclassRef).
+    e. If superclass is null, then
+      [...]
+    f. Else if IsConstructor(superclass) is false, throw a TypeError exception.
+features: [async-functions, class, Proxy]
+---*/
+
+async function fn() {}
+Object.defineProperty(fn, "prototype", {
+  get: function() {
+    throw new Test262Error("`superclass.prototype` is unreachable");
+  },
+});
+
+assert.throws(TypeError, function() {
+  class A extends fn {}
+});
+
+var bound = (async function() {}).bind();
+Object.defineProperty(bound, "prototype", {
+  get: function() {
+    throw new Test262Error("`superclass.prototype` is unreachable");
+  },
+});
+
+assert.throws(TypeError, function() {
+  class C extends bound {}
+});
+
+var proxy = new Proxy(async function() {}, {
+  get: function() {
+    throw new Test262Error("`superclass.prototype` is unreachable");
+  },
+});
+
+assert.throws(TypeError, function() {
+  class C extends proxy {}
+});