stream-flow-control/tests/flows/first.test.js

Stream Flow Control

const {FlowFirst} = require('../../lib');
const {Readable, Transform, Writable} = require('stream');

describe('FlowFirst test', () => {

    test('Flows the first message that arrives', done => {
        const start = Readable.from(['{"id": 1}', '{"id": 2}', '{"id": 3}']);

        let results = {};
        
        const transform1 = new Transform({
            objectMode: true,
            transform(chunk, encoding, callback) {
                const obj = JSON.parse(chunk);
                obj.from = 1;
                if(obj.id !== 1) {
                    setTimeout(()=> {
                        this.push(obj);
                        callback();
                    }, 150);
                } else {
                    this.push(obj);
                    callback();
                }
            }
        });
        const transform2 = new Transform({
            objectMode: true,
            transform(chunk, encoding, callback) {
                const obj = JSON.parse(chunk);
                obj.from = 2;
                if(obj.id !== 2) {
                    setTimeout(()=> {
                        this.push(obj);
                        callback();
                    }, 120);
                } else {
                    this.push(obj);
                    callback();
                }
            }
        });
        const transform3 = new Transform({
            objectMode: true,
            transform(chunk, encoding, callback) {
                const obj = JSON.parse(chunk);
                obj.from = 3;
                if(obj.id !== 3) {
                    setTimeout(()=> {
                        this.push(obj);
                        callback();
                    }, 100);
                } else {
                    this.push(obj);
                    callback();
                }
            }
        });

        const checkFinish = () => {
            expect(results).toEqual({m1: 1, m2: 2, m3: 3});
            done();
        };

        const writeStream = new Writable({
            objectMode: true,
            write(chunk, encoding, callback) {
                results[`m${chunk.id}`] = chunk.from;
                callback();
            }
        });
        writeStream.on('finish', checkFinish);
        
        const flow = new FlowFirst({
            identify(payload) {
                return payload.id;
            }
        });
        flow.pipe(writeStream);
        start.pipe(transform1).pipe(flow);
        start.pipe(transform2).pipe(flow);
        start.pipe(transform3).pipe(flow);
    });

});