LibJS: Implement Temporal.Calendar.prototype.fields()

Userland/Libraries/LibJS/Tests/builtins/Temporal/Calendar/Calendar.prototype.fields.js

@@ -0,0 +1,30 @@
+describe("correct behavior", () => {
+    test("length is 1", () => {
+        expect(Temporal.Calendar.prototype.fields).toHaveLength(1);
+    });
+
+    test("basic functionality", () => {
+        const calendar = new Temporal.Calendar("iso8601");
+        const array = ["foo", "bar", "baz"];
+        const fields = calendar.fields(array);
+        expect(fields).toEqual(array);
+        expect(fields).not.toBe(array);
+    });
+});
+
+describe("errors", () => {
+    test("this value must be a Temporal.Calendar object", () => {
+        expect(() => {
+            Temporal.Calendar.prototype.fields.call("foo");
+        }).toThrowWithMessage(TypeError, "Not a Temporal.Calendar");
+    });
+
+    test("iterator values must be strings", () => {
+        const calendar = new Temporal.Calendar("iso8601");
+        for (const value of [123, null, undefined, true, {}]) {
+            expect(() => {
+                calendar.fields([value]);
+            }).toThrowWithMessage(TypeError, "FIXME: Add a string for this error.");
+        }
+    });
+});