NativeScript/unit-tests/observable/observable.ts

import { Observable } from "tns-core-modules/data/observable";
import { assert } from "chai";

describe("observable", () => {
    describe("once", () => {

        let observable: Observable;
        let handler: () => void;
        let callCount: number = 0;

        beforeEach("create handlers", () => {
            handler = function() {
                callCount++;
            }
            observable = new Observable();
            observable.once("test", handler);
        });
        afterEach("reset handlers", () => {
            callCount = 0;
            handler = null;
            observable = null;
        });

        function notify() {
            observable.notify({ eventName: "test", object: observable });
        }
        function notifyWrong() {
            observable.notify({ eventName: "test2", object: observable });
        }

        it("fires just once", () => {
            notify();
            notify();
            assert.equal(callCount, 1, "Expected the handler to be called exactly once");
        });
        it("does not fire for other events", () => {
            notifyWrong();
            assert.equal(callCount, 0, "Expected the handler to not be called, when other events fire");
        });
    });

    describe("once", () => {
        it("fire once when fired recursively", () => {
            const observable = new Observable();
            let callCount1 = 0;
            let callCount2 = 0;
            const handler2 = function () {
                callCount2++;
            }
            const handler1 = function () {
                callCount1++;
                observable.once("test", handler2);
                observable.notify({ eventName: "test", object: observable });
            }
            observable.once("test", handler1);
            observable.notify({ eventName: "test", object: observable });
            assert.equal(callCount1, 1, "Expected the first handler to unsubscribe before being fired and to notify just once");
            assert.equal(callCount2, 1, "Expected the second handler to be fired once when recursively notified by the first handler");
        });
    });
});