LibJS: Add most of the Set.prototype methods

Specifically all aside from "values" and "entries" which require an
implementation of the SetIterator object.

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

@@ -27,5 +27,10 @@ describe("normal behavior", () => {
         var a = new Set([0, 1, 2]);
         expect(a instanceof Set).toBeTrue();
         expect(a).toHaveSize(3);
+        var seen = [false, false, false];
+        a.forEach(x => {
+            seen[x] = true;
+        });
+        expect(seen[0] && seen[1] && seen[2]);
     });
 });

Userland/Libraries/LibJS/Tests/builtins/Set/Set.prototype.add.js

@@ -0,0 +1,10 @@
+test("basic functionality", () => {
+    expect(Set.prototype.add).toHaveLength(1);
+
+    const set = new Set(["a", "b", "c"]);
+    expect(set).toHaveSize(3);
+    expect(set.add("d")).toBe(set);
+    expect(set).toHaveSize(4);
+    expect(set.add("a")).toBe(set);
+    expect(set).toHaveSize(4);
+});

Userland/Libraries/LibJS/Tests/builtins/Set/Set.prototype.clear.js

@@ -0,0 +1,8 @@
+test("basic functionality", () => {
+    expect(Set.prototype.clear).toHaveLength(0);
+
+    const set = new Set(["a", "b", "c"]);
+    expect(set).toHaveSize(3);
+    set.clear();
+    expect(set).toHaveSize(0);
+});

Userland/Libraries/LibJS/Tests/builtins/Set/Set.prototype.delete.js

@@ -0,0 +1,10 @@
+test("basic functionality", () => {
+    expect(Set.prototype.delete).toHaveLength(1);
+
+    const set = new Set(["a", "b", "c"]);
+    expect(set).toHaveSize(3);
+    expect(set.delete("b")).toBeTrue();
+    expect(set).toHaveSize(2);
+    expect(set.delete("b")).toBeFalse();
+    expect(set).toHaveSize(2);
+});

Userland/Libraries/LibJS/Tests/builtins/Set/Set.prototype.forEach.js

@@ -0,0 +1,48 @@
+test("length is 1", () => {
+    expect(Set.prototype.forEach).toHaveLength(1);
+});
+
+describe("errors", () => {
+    test("requires at least one argument", () => {
+        expect(() => {
+            new Set().forEach();
+        }).toThrowWithMessage(TypeError, "undefined is not a function");
+    });
+
+    test("callback must be a function", () => {
+        expect(() => {
+            new Set().forEach(undefined);
+        }).toThrowWithMessage(TypeError, "undefined is not a function");
+    });
+});
+
+describe("normal behavior", () => {
+    test("never calls callback with empty set", () => {
+        var callbackCalled = 0;
+        expect(
+            new Set().forEach(() => {
+                callbackCalled++;
+            })
+        ).toBeUndefined();
+        expect(callbackCalled).toBe(0);
+    });
+
+    test("calls callback once for every item", () => {
+        var callbackCalled = 0;
+        expect(
+            new Set([1, 2, 3]).forEach(() => {
+                callbackCalled++;
+            })
+        ).toBeUndefined();
+        expect(callbackCalled).toBe(3);
+    });
+
+    test("callback receives value twice and set", () => {
+        var a = new Set([1, 2, 3]);
+        a.forEach((value1, value2, set) => {
+            expect(a.has(value1)).toBeTrue();
+            expect(value1).toBe(value2);
+            expect(set).toBe(a);
+        });
+    });
+});

Userland/Libraries/LibJS/Tests/builtins/Set/Set.prototype.has.js

@@ -0,0 +1,13 @@
+test("length is 1", () => {
+    expect(Set.prototype.has).toHaveLength(1);
+});
+
+test("basic functionality", () => {
+    var set = new Set(["hello", "friends", 1, 2, false]);
+
+    expect(new Set().has()).toBeFalse();
+    expect(new Set([undefined]).has()).toBeTrue();
+    expect(set.has("hello")).toBeTrue();
+    expect(set.has(1)).toBeTrue();
+    expect(set.has("serenity")).toBeFalse();
+});