LibJS: Add the WeakRef built-in object

Userland/Libraries/LibJS/Tests/builtins/WeakRef/WeakRef.js

@@ -0,0 +1,30 @@
+test("constructor properties", () => {
+    expect(WeakRef).toHaveLength(1);
+    expect(WeakRef.name).toBe("WeakRef");
+});
+
+describe("errors", () => {
+    test("invalid array iterators", () => {
+        [-100, Infinity, NaN, 152n, undefined].forEach(value => {
+            expect(() => {
+                new WeakRef(value);
+            }).toThrowWithMessage(TypeError, "is not an object");
+        });
+    });
+    test("called without new", () => {
+        expect(() => {
+            WeakRef();
+        }).toThrowWithMessage(TypeError, "WeakRef constructor must be called with 'new'");
+    });
+});
+
+describe("normal behavior", () => {
+    test("typeof", () => {
+        expect(typeof new WeakRef({})).toBe("object");
+    });
+
+    test("constructor with single object argument", () => {
+        var a = new WeakRef({});
+        expect(a instanceof WeakRef).toBeTrue();
+    });
+});