LibJS: Implement Object.assign()

Userland/Libraries/LibJS/Tests/builtins/Object/Object.assign.js

@@ -0,0 +1,42 @@
+test("length is 2", () => {
+    expect(Object.assign).toHaveLength(2);
+});
+
+describe("errors", () => {
+    test("first argument must coercible to object", () => {
+        expect(() => {
+            Object.assign(null);
+        }).toThrowWithMessage(TypeError, "ToObject on null or undefined");
+        expect(() => {
+            Object.assign(undefined);
+        }).toThrowWithMessage(TypeError, "ToObject on null or undefined");
+    });
+});
+
+describe("normal behavior", () => {
+    test("returns first argument coerced to object", () => {
+        const o = {};
+        expect(Object.assign(o)).toBe(o);
+        expect(Object.assign(o, {})).toBe(o);
+        expect(Object.assign(42)).toEqual(new Number(42));
+    });
+
+    test("alters first argument object if sources are given", () => {
+        const o = { foo: 0 };
+        expect(Object.assign(o, { foo: 1 })).toBe(o);
+        expect(o).toEqual({ foo: 1 });
+    });
+
+    test("merges objects", () => {
+        const s = Symbol();
+        expect(
+            Object.assign(
+                {},
+                { foo: 0, bar: "baz" },
+                { [s]: [1, 2, 3] },
+                { foo: 1 },
+                { [42]: "test" }
+            )
+        ).toEqual({ foo: 1, bar: "baz", [s]: [1, 2, 3], 42: "test" });
+    });
+});