LibJS: Implement Temporal.PlainYearMonth.prototype.with()

Userland/Libraries/LibJS/Tests/builtins/Temporal/PlainYearMonth/PlainYearMonth.prototype.with.js

@@ -0,0 +1,57 @@
+describe("correct behavior", () => {
+    test("length is 1", () => {
+        expect(Temporal.PlainYearMonth.prototype.with).toHaveLength(1);
+    });
+
+    test("basic functionality", () => {
+        const plainYearMonth = new Temporal.PlainYearMonth(1970, 1);
+        const values = [
+            [{ year: 2021 }, new Temporal.PlainYearMonth(2021, 1)],
+            [{ year: 2021, month: 7 }, new Temporal.PlainYearMonth(2021, 7)],
+            [{ year: 2021, monthCode: "M07" }, new Temporal.PlainYearMonth(2021, 7)],
+        ];
+        for (const [arg, expected] of values) {
+            expect(plainYearMonth.with(arg).equals(expected)).toBeTrue();
+        }
+
+        // Supplying the same values doesn't change the year/month, but still creates a new object
+        const plainYearMonthLike = { year: plainYearMonth.year, month: plainYearMonth.month };
+        expect(plainYearMonth.with(plainYearMonthLike)).not.toBe(plainYearMonth);
+        expect(plainYearMonth.with(plainYearMonthLike).equals(plainYearMonth)).toBeTrue();
+    });
+});
+
+describe("errors", () => {
+    test("this value must be a Temporal.PlainYearMonth object", () => {
+        expect(() => {
+            Temporal.PlainYearMonth.prototype.with.call("foo");
+        }).toThrowWithMessage(TypeError, "Not an object of type Temporal.PlainYearMonth");
+    });
+
+    test("argument must be an object", () => {
+        expect(() => {
+            new Temporal.PlainYearMonth(1970, 1).with("foo");
+        }).toThrowWithMessage(TypeError, "foo is not an object");
+        expect(() => {
+            new Temporal.PlainYearMonth(1970, 1).with(42);
+        }).toThrowWithMessage(TypeError, "42 is not an object");
+    });
+
+    test("argument must have one of 'month', 'monthCode', 'year'", () => {
+        expect(() => {
+            new Temporal.PlainYearMonth(1970, 1).with({});
+        }).toThrowWithMessage(
+            TypeError,
+            "Object must have at least one of the following properties: month, monthCode, year"
+        );
+    });
+
+    test("argument must not have 'calendar' or 'timeZone'", () => {
+        expect(() => {
+            new Temporal.PlainYearMonth(1970, 1).with({ calendar: {} });
+        }).toThrowWithMessage(TypeError, "Object must not have a defined calendar property");
+        expect(() => {
+            new Temporal.PlainYearMonth(1970, 1).with({ timeZone: {} });
+        }).toThrowWithMessage(TypeError, "Object must not have a defined timeZone property");
+    });
+});