Add tests for ShadowRealmGlobalScope.self attribute

Ref: https://whatpr.org/html/9893/c0fbcc2...ea3c573/webappapis.html#the-shadowrealmglobalscope-interface

Author: ptomato

html/webappapis/the-shadowrealmglobalscope-interface/self.any.js

@@ -0,0 +1,48 @@
+// META: title=The self attribute
+// META: global=shadowrealm
+
+test(() => {
+  assert_equals(self, globalThis, "self should be the same object as globalThis");
+}, "self attribute is the global object");
+
+test(() => {
+  assert_equals(self, self.self, "self should be the same object as self.self");
+}, "self attribute is the object itself");
+
+test(() => {
+  assert_own_property(globalThis, "self", "self should be an own property");
+  assert_readonly(globalThis, "self", "self should be a read-only property");
+}, "self is a readonly attribute");
+
+test(() => {
+  // https://webidl.spec.whatwg.org/#define-the-attributes
+  const descr = Object.getOwnPropertyDescriptor(self, "self");
+  assert_equals(descr.value, undefined, "self should be an accessor property");
+  assert_true(descr.enumerable, "self should be enumerable");
+  assert_true(descr.configurable, "self should be configurable");
+}, "self property descriptor");
+
+test(() => {
+  const getter = Object.getOwnPropertyDescriptor(self, "self").get;
+  assert_equals(getter.name, "get self", "function should be named 'get self'");
+}, "self getter name");
+
+test(() => {
+  const getter = Object.getOwnPropertyDescriptor(self, "self").get;
+  assert_equals(getter.length, 0, "function should take 0 arguments");
+}, "self getter length");
+
+test(() => {
+  // https://webidl.spec.whatwg.org/#dfn-attribute-getter
+  const getter = Object.getOwnPropertyDescriptor(self, "self").get;
+
+  assert_throws_js(TypeError, () => getter.call({}),
+    "the self getter should fail a brand check if it's an object not implementing ShadowRealmGlobalScope");
+  assert_throws_js(TypeError, () => getter.call(42),
+    "the self getter should fail a brand check if a primitive");
+
+  assert_equals(getter.call(null), self,
+    "the self getter's this object should fall back to the realm's global object if null");
+  assert_equals(getter.call(undefined), self,
+    "the self getter's this object should fall back to the realm's global object if undefined");
+}, "self getter steps");