Test RegExp.prototype.toString called as top-level function

test/built-ins/RegExp/prototype/toString/called-as-function.js

@@ -0,0 +1,32 @@
+// Copyright (C) 2020 Alexey Shvayka. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-regexp.prototype.tostring
+description: >
+    `this` value is resolved using strict mode semantics,
+    throwing TypeError if called as top-level function.
+info: |
+    RegExp.prototype.toString ( )
+
+    1. Let R be the this value.
+    2. If Type(R) is not Object, throw a TypeError exception.
+
+    ToObject ( argument )
+
+    Argument Type: Undefined
+    Result: Throw a TypeError exception.
+---*/
+
+["source", "flags"].forEach(function(key) {
+    Object.defineProperty(this, key, {
+        get: function() {
+            throw new Test262Error(key + " lookup should not be performed");
+        },
+    });
+}, this);
+
+var toString = RegExp.prototype.toString;
+assert.throws(TypeError, function() {
+    toString();
+});