LibJS: Add Date.prototype.setMonth()

Author: https://github.com/IdanHo
Commit: a93b1c7ea0
Pull-request: https://github.com/SerenityOS/serenity/pull/7845
Reviewed-by: https://github.com/linusg

Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.setMonth.js

@@ -0,0 +1,87 @@
+test("no arguments", () => {
+    let date = new Date(2021, 0, 1);
+    date.setMonth();
+    expect(date.getTime()).toBe(NaN);
+});
+
+test("NaN or undefined as only argument", () => {
+    let date = new Date(2021, 0, 1);
+    date.setMonth(NaN);
+    expect(date.getTime()).toBe(NaN);
+
+    date = new Date(2021, 0, 1);
+    date.setMonth(undefined);
+    expect(date.getTime()).toBe(NaN);
+
+    date = new Date(2021, 0, 1);
+    date.setMonth("a");
+    expect(date.getTime()).toBe(NaN);
+});
+
+test("Only month as argument", () => {
+    let date = new Date(2021, 0, 1);
+
+    date.setMonth(7);
+    expect(date.getFullYear()).toBe(2021);
+    expect(date.getMonth()).toBe(7);
+    expect(date.getDate()).toBe(1);
+    expect(date.getHours()).toBe(0);
+    expect(date.getMinutes()).toBe(0);
+    expect(date.getSeconds()).toBe(0);
+    expect(date.getMilliseconds()).toBe(0);
+});
+
+test("Month and date as arguments", () => {
+    let date = new Date(2021, 0, 1);
+
+    date.setMonth(7, 3);
+    expect(date.getFullYear()).toBe(2021);
+    expect(date.getMonth()).toBe(7);
+    expect(date.getDate()).toBe(3);
+    expect(date.getHours()).toBe(0);
+    expect(date.getMinutes()).toBe(0);
+    expect(date.getSeconds()).toBe(0);
+    expect(date.getMilliseconds()).toBe(0);
+});
+
+test("NaN or undefined in any arguments", () => {
+    let date = new Date(2021, 0, 1);
+    date.setMonth(NaN, 3);
+    expect(date.getTime()).toBe(NaN);
+
+    date = new Date(2021, 0, 1);
+    date.setMonth(2021, NaN);
+    expect(date.getTime()).toBe(NaN);
+
+    date = new Date(2021, 0, 1);
+    date.setMonth(undefined, 3);
+    expect(date.getTime()).toBe(NaN);
+
+    date = new Date(2021, 0, 1);
+    date.setMonth(2021, undefined);
+    expect(date.getTime()).toBe(NaN);
+
+    date.setMonth(3, 16);
+    expect(date.getFullYear()).toBe(2021);
+    expect(date.getMonth()).toBe(3);
+    expect(date.getDate()).toBe(16);
+    expect(date.getHours()).toBe(0);
+    expect(date.getMinutes()).toBe(0);
+    expect(date.getSeconds()).toBe(0);
+    expect(date.getMilliseconds()).toBe(0);
+});
+
+test("Make Invalid Date valid again", () => {
+    let date = new Date(2021, 0, 1);
+    date.setMonth(NaN, 3, 16);
+    expect(date.getTime()).toBe(NaN);
+
+    date.setMonth(3, 16);
+    expect(date.getFullYear()).toBe(2021);
+    expect(date.getMonth()).toBe(3);
+    expect(date.getDate()).toBe(16);
+    expect(date.getHours()).toBe(0);
+    expect(date.getMinutes()).toBe(0);
+    expect(date.getSeconds()).toBe(0);
+    expect(date.getMilliseconds()).toBe(0);
+});