stream-chain/tests/test_demo.js

'use strict';

const unit = require('heya-unit');

const {Transform} = require('stream');

const chain = require('../src/index');
const fromIterable = require('../src/utils/fromIterable');

const getTotalFromDatabaseByKey = async x =>
new Promise(resolve => {
  setTimeout(() => {
    resolve(Math.min(x % 10, 3));
  }, 20);
});

unit.add(module, [
  function test_demo(t) {
    const async = t.startAsync('test_demo');

    const c = chain([
        // transforms a value
        x => x * x,
        // returns several values
        x => chain.many([x - 1, x, x + 1]),
        // waits for an asynchronous operation
        async x => await getTotalFromDatabaseByKey(x),
        // returns multiple values with a generator
        function* (x) {
          for (let i = x; i > 0; --i) {
            yield i;
          }
          return 0;
        },
        // filters out even values
        x => (x % 2 ? x : null),
        // uses an arbitrary transform stream
        new Transform({
          objectMode: true,
          transform(x, _, callback) {
            callback(null, x + 1);
          }
        })
      ]),
      output = [];
    c.on('data', data => output.push(data));
    c.on('end', () => {
      eval(t.TEST('t.unify(output, [2, 2, 4, 2, 4, 2, 4, 2, 4, 2, 4, 2])'));
      async.done();
    });

    fromIterable([1, 2, 3]).pipe(c);
  },
  function test_demoNoGrouping(t) {
    const async = t.startAsync('test_demoNoGrouping');

    const c = chain([
        // transforms a value
        x => x * x,
        // returns several values
        x => chain.many([x - 1, x, x + 1]),
        // waits for an asynchronous operation
        async x => await getTotalFromDatabaseByKey(x),
        // returns multiple values with a generator
        function* (x) {
          for (let i = x; i > 0; --i) {
            yield i;
          }
          return 0;
        },
        // filters out even values
        x => (x % 2 ? x : null),
        // uses an arbitrary transform stream
        new Transform({
          objectMode: true,
          transform(x, _, callback) {
            callback(null, x + 1);
          }
        })
      ], {noGrouping: true}),
      output = [];
    c.on('data', data => output.push(data));
    c.on('end', () => {
      eval(t.TEST('t.unify(output, [2, 2, 4, 2, 4, 2, 4, 2, 4, 2, 4, 2])'));
      async.done();
    });

    fromIterable([1, 2, 3]).pipe(c);
  }
]);