event-emitters/dist.es2018/QueueingEventEmitter.spec.js

event emitters

import { QueueingEventEmitter } from '.';
describe('QueueingEventEmitter', () => {
    const createEventEmitter = () => new QueueingEventEmitter();
    let emitter = createEventEmitter();
    beforeEach(() => {
        emitter = createEventEmitter();
    });
    it('queues messages when there are no subscribers and emits them to first subscriber', () => {
        const subscriber = jest.fn();
        emitter.emit('one');
        emitter.emit('two');
        emitter.subscribe(subscriber);
        expect(subscriber.mock.calls).toEqual([['one'], ['two']]);
    });
    it('stops queueing messages when there is a subscriber', () => {
        const subscriber = jest.fn();
        emitter.emit('one');
        emitter.emit('two');
        emitter.subscribe(subscriber);
        expect(subscriber.mock.calls).toEqual([['one'], ['two']]);
        emitter.emit('three');
        expect(subscriber.mock.calls).toEqual([['one'], ['two'], ['three']]);
    });
    it('resumes queueing message when it loses all subscribers', () => {
        const subscriber1 = jest.fn();
        const subscriber2 = jest.fn();
        emitter.emit('one');
        emitter.emit('two');
        emitter.subscribe(subscriber1);
        emitter.subscribe(subscriber2);
        expect(subscriber1.mock.calls).toEqual([['one'], ['two']]);
        expect(subscriber2).toHaveBeenCalledTimes(0);
        emitter.emit('three');
        expect(subscriber1.mock.calls).toEqual([['one'], ['two'], ['three']]);
        expect(subscriber2.mock.calls).toEqual([['three']]);
        emitter.unsubscribe(subscriber1);
        emitter.emit('four');
        expect(subscriber1).toHaveBeenCalledTimes(3);
        expect(subscriber2.mock.calls).toEqual([['three'], ['four']]);
        emitter.unsubscribe(subscriber2);
        emitter.emit('five');
        emitter.emit('six');
        const subscriber3 = jest.fn();
        emitter.subscribe(subscriber3);
        expect(subscriber3.mock.calls).toEqual([['five'], ['six']]);
        emitter.emit('seven');
        expect(subscriber3.mock.calls).toEqual([['five'], ['six'], ['seven']]);
    });
    it('re-throws the final error when the subscriber throws during queue drain', () => {
        const subscriber1 = jest
            .fn()
            .mockImplementationOnce(() => {
            throw new Error('1');
        })
            .mockImplementationOnce(() => {
            throw new Error('2');
        });
        emitter.emit('one');
        emitter.emit('two');
        emitter.emit('three');
        expect(() => {
            emitter.subscribe(subscriber1);
        }).toThrow('2');
        // make sure the queue is drained
        const subscriber2 = jest.fn();
        emitter.subscribe(subscriber2);
        expect(subscriber2).toHaveBeenCalledTimes(0);
    });
});
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