Add [[PreventExtensions]] tests

test/built-ins/Proxy/preventExtensions/trap-is-missing-target-is-proxy.js

@@ -0,0 +1,30 @@
+// Copyright (C) 2020 Alexey Shvayka. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-proxy-object-internal-methods-and-internal-slots-preventextensions
+description: >
+  If "preventExtensions" trap is null or undefined, [[PreventExtensions]] call
+  is properly forwarded to [[ProxyTarget]] (which is also a Proxy object).
+info: |
+  [[PreventExtensions]] ( )
+
+  [...]
+  4. Let target be O.[[ProxyTarget]].
+  5. Let trap be ? GetMethod(handler, "preventExtensions").
+  6. If trap is undefined, then
+    a. Return ? target.[[PreventExtensions]]().
+features: [Proxy]
+---*/
+
+var target = new Proxy({}, {
+  preventExtensions: function(_target) {
+    return false;
+  },
+});
+
+var proxy = new Proxy(target, {});
+
+assert.throws(TypeError, function() {
+  Object.preventExtensions(proxy);
+});

test/built-ins/Proxy/preventExtensions/trap-is-null-target-is-proxy.js

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+// Copyright (C) 2020 Alexey Shvayka. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-proxy-object-internal-methods-and-internal-slots-preventextensions
+description: >
+  If "preventExtensions" trap is null or undefined, [[PreventExtensions]] call
+  is properly forwarded to [[ProxyTarget]] (which is also a Proxy object).
+info: |
+  [[PreventExtensions]] ( )
+
+  [...]
+  4. Let target be O.[[ProxyTarget]].
+  5. Let trap be ? GetMethod(handler, "preventExtensions").
+  6. If trap is undefined, then
+    a. Return ? target.[[PreventExtensions]]().
+features: [Proxy]
+---*/
+
+var plainObject = {};
+var plainObjectTarget = new Proxy(plainObject, {});
+var plainObjectProxy = new Proxy(plainObjectTarget, {
+  preventExtensions: null,
+});
+
+Object.preventExtensions(plainObjectProxy);
+assert(!Object.isExtensible(plainObject));

test/built-ins/Proxy/preventExtensions/trap-is-undefined-target-is-proxy.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-proxy-object-internal-methods-and-internal-slots-preventextensions
+description: >
+  If "preventExtensions" trap is null or undefined, [[PreventExtensions]] call
+  is properly forwarded to [[ProxyTarget]] (which is also a Proxy object).
+info: |
+  [[PreventExtensions]] ( )
+
+  [...]
+  4. Let target be O.[[ProxyTarget]].
+  5. Let trap be ? GetMethod(handler, "preventExtensions").
+  6. If trap is undefined, then
+    a. Return ? target.[[PreventExtensions]]().
+
+  [[PreventExtensions]] ( )
+
+  1. Return true.
+features: [Proxy, Reflect]
+flags: [module]
+---*/
+
+import * as ns from "./trap-is-undefined-target-is-proxy.js";
+
+var nsTarget = new Proxy(ns, {});
+var nsProxy = new Proxy(nsTarget, {
+  preventExtensions: undefined,
+});
+
+assert(Reflect.preventExtensions(nsProxy));