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Stream: New utility library for iterables
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Richard Hansen
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2 changed files with 492 additions and 0 deletions
358
src/tests/backend/specs/Stream.js
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358
src/tests/backend/specs/Stream.js
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'use strict';
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const Stream = require('../../../node/utils/Stream');
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const assert = require('assert').strict;
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class DemoIterable {
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constructor() {
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this.value = 0;
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this.errs = [];
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this.rets = [];
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}
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completed() { return this.errs.length > 0 || this.rets.length > 0; }
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next() {
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if (this.completed()) return {value: undefined, done: true}; // Mimic standard generators.
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return {value: this.value++, done: false};
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}
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throw(err) {
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const alreadyCompleted = this.completed();
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this.errs.push(err);
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if (alreadyCompleted) throw err; // Mimic standard generator objects.
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throw err;
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}
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return(ret) {
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const alreadyCompleted = this.completed();
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this.rets.push(ret);
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if (alreadyCompleted) return {value: ret, done: true}; // Mimic standard generator objects.
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return {value: ret, done: true};
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}
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[Symbol.iterator]() { return this; }
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}
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const assertUnhandledRejection = async (action, want) => {
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// Temporarily remove unhandled Promise rejection listeners so that the unhandled rejections we
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// expect to see don't trigger a test failure (or terminate node).
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const event = 'unhandledRejection';
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const listenersBackup = process.rawListeners(event);
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process.removeAllListeners(event);
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let tempListener;
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let asyncErr;
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try {
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const seenErrPromise = new Promise((resolve) => {
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tempListener = (err) => {
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assert.equal(asyncErr, undefined);
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asyncErr = err;
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resolve();
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};
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});
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process.on(event, tempListener);
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await action();
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await seenErrPromise;
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} finally {
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// Restore the original listeners.
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process.off(event, tempListener);
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for (const listener of listenersBackup) process.on(event, listener);
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}
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await assert.rejects(Promise.reject(asyncErr), want);
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};
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describe(__filename, function () {
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describe('basic behavior', function () {
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it('takes a generator', async function () {
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assert.deepEqual([...new Stream((function* () { yield 0; yield 1; yield 2; })())], [0, 1, 2]);
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});
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it('takes an array', async function () {
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assert.deepEqual([...new Stream([0, 1, 2])], [0, 1, 2]);
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});
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it('takes an iterator', async function () {
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assert.deepEqual([...new Stream([0, 1, 2][Symbol.iterator]())], [0, 1, 2]);
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});
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it('supports empty iterators', async function () {
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assert.deepEqual([...new Stream([])], []);
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});
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it('is resumable', async function () {
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const s = new Stream((function* () { yield 0; yield 1; yield 2; })());
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let iter = s[Symbol.iterator]();
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assert.deepEqual(iter.next(), {value: 0, done: false});
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iter = s[Symbol.iterator]();
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assert.deepEqual(iter.next(), {value: 1, done: false});
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assert.deepEqual([...s], [2]);
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});
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it('supports return value', async function () {
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const s = new Stream((function* () { yield 0; return 1; })());
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const iter = s[Symbol.iterator]();
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assert.deepEqual(iter.next(), {value: 0, done: false});
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assert.deepEqual(iter.next(), {value: 1, done: true});
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});
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it('does not start until needed', async function () {
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let lastYield = null;
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new Stream((function* () { yield lastYield = 0; })());
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// Fetching from the underlying iterator should not start until the first value is fetched
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// from the stream.
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assert.equal(lastYield, null);
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});
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it('throw is propagated', async function () {
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const underlying = new DemoIterable();
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const s = new Stream(underlying);
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const iter = s[Symbol.iterator]();
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assert.deepEqual(iter.next(), {value: 0, done: false});
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const err = new Error('injected');
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assert.throws(() => iter.throw(err), err);
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assert.equal(underlying.errs[0], err);
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});
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it('return is propagated', async function () {
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const underlying = new DemoIterable();
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const s = new Stream(underlying);
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const iter = s[Symbol.iterator]();
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assert.deepEqual(iter.next(), {value: 0, done: false});
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assert.deepEqual(iter.return(42), {value: 42, done: true});
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assert.equal(underlying.rets[0], 42);
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});
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});
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describe('range', function () {
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it('basic', async function () {
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assert.deepEqual([...Stream.range(0, 3)], [0, 1, 2]);
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});
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it('empty', async function () {
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assert.deepEqual([...Stream.range(0, 0)], []);
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});
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it('positive start', async function () {
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assert.deepEqual([...Stream.range(3, 5)], [3, 4]);
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});
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it('negative start', async function () {
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assert.deepEqual([...Stream.range(-3, 0)], [-3, -2, -1]);
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});
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it('end before start', async function () {
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assert.deepEqual([...Stream.range(3, 0)], []);
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});
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});
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describe('batch', function () {
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it('empty', async function () {
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assert.deepEqual([...new Stream([]).batch(10)], []);
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});
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it('does not start until needed', async function () {
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let lastYield = null;
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new Stream((function* () { yield lastYield = 0; })()).batch(10);
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assert.equal(lastYield, null);
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});
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it('fewer than batch size', async function () {
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let lastYield = null;
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const values = (function* () {
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for (let i = 0; i < 5; i++) yield lastYield = i;
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})();
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const s = new Stream(values).batch(10);
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assert.equal(lastYield, null);
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assert.deepEqual(s[Symbol.iterator]().next(), {value: 0, done: false});
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assert.equal(lastYield, 4);
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assert.deepEqual([...s], [1, 2, 3, 4]);
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assert.equal(lastYield, 4);
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});
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it('exactly batch size', async function () {
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let lastYield = null;
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const values = (function* () {
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for (let i = 0; i < 5; i++) yield lastYield = i;
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})();
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const s = new Stream(values).batch(5);
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assert.equal(lastYield, null);
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assert.deepEqual(s[Symbol.iterator]().next(), {value: 0, done: false});
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assert.equal(lastYield, 4);
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assert.deepEqual([...s], [1, 2, 3, 4]);
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assert.equal(lastYield, 4);
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});
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it('multiple batches, last batch is not full', async function () {
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let lastYield = null;
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const values = (function* () {
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for (let i = 0; i < 10; i++) yield lastYield = i;
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})();
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const s = new Stream(values).batch(3);
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assert.equal(lastYield, null);
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const iter = s[Symbol.iterator]();
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assert.deepEqual(iter.next(), {value: 0, done: false});
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assert.equal(lastYield, 2);
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assert.deepEqual(iter.next(), {value: 1, done: false});
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assert.deepEqual(iter.next(), {value: 2, done: false});
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assert.equal(lastYield, 2);
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assert.deepEqual(iter.next(), {value: 3, done: false});
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assert.equal(lastYield, 5);
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assert.deepEqual([...s], [4, 5, 6, 7, 8, 9]);
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assert.equal(lastYield, 9);
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});
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it('batched Promise rejections are suppressed while iterating', async function () {
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let lastYield = null;
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const err = new Error('injected');
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const values = (function* () {
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lastYield = 'promise of 0';
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yield new Promise((resolve) => setTimeout(() => resolve(0), 100));
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lastYield = 'rejected Promise';
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yield Promise.reject(err);
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lastYield = 'promise of 2';
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yield Promise.resolve(2);
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})();
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const s = new Stream(values).batch(3);
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const iter = s[Symbol.iterator]();
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const nextp = iter.next().value;
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assert.equal(lastYield, 'promise of 2');
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assert.equal(await nextp, 0);
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await assert.rejects(iter.next().value, err);
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iter.return();
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});
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it('batched Promise rejections are unsuppressed when iteration completes', async function () {
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let lastYield = null;
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const err = new Error('injected');
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const values = (function* () {
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lastYield = 'promise of 0';
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yield new Promise((resolve) => setTimeout(() => resolve(0), 100));
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lastYield = 'rejected Promise';
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yield Promise.reject(err);
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lastYield = 'promise of 2';
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yield Promise.resolve(2);
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})();
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const s = new Stream(values).batch(3);
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const iter = s[Symbol.iterator]();
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assert.equal(await iter.next().value, 0);
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assert.equal(lastYield, 'promise of 2');
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await assertUnhandledRejection(() => iter.return(), err);
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});
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});
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describe('buffer', function () {
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it('empty', async function () {
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assert.deepEqual([...new Stream([]).buffer(10)], []);
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});
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it('does not start until needed', async function () {
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let lastYield = null;
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new Stream((function* () { yield lastYield = 0; })()).buffer(10);
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assert.equal(lastYield, null);
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});
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it('fewer than buffer size', async function () {
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let lastYield = null;
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const values = (function* () {
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for (let i = 0; i < 5; i++) yield lastYield = i;
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})();
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const s = new Stream(values).buffer(10);
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assert.equal(lastYield, null);
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assert.deepEqual(s[Symbol.iterator]().next(), {value: 0, done: false});
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assert.equal(lastYield, 4);
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assert.deepEqual([...s], [1, 2, 3, 4]);
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assert.equal(lastYield, 4);
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});
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it('exactly buffer size', async function () {
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let lastYield = null;
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const values = (function* () {
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for (let i = 0; i < 5; i++) yield lastYield = i;
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})();
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const s = new Stream(values).buffer(5);
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assert.equal(lastYield, null);
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assert.deepEqual(s[Symbol.iterator]().next(), {value: 0, done: false});
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assert.equal(lastYield, 4);
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assert.deepEqual([...s], [1, 2, 3, 4]);
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assert.equal(lastYield, 4);
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});
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it('more than buffer size', async function () {
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let lastYield = null;
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const values = (function* () {
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for (let i = 0; i < 10; i++) yield lastYield = i;
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})();
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const s = new Stream(values).buffer(3);
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assert.equal(lastYield, null);
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const iter = s[Symbol.iterator]();
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assert.deepEqual(iter.next(), {value: 0, done: false});
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assert.equal(lastYield, 3);
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assert.deepEqual(iter.next(), {value: 1, done: false});
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assert.equal(lastYield, 4);
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assert.deepEqual(iter.next(), {value: 2, done: false});
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assert.equal(lastYield, 5);
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assert.deepEqual([...s], [3, 4, 5, 6, 7, 8, 9]);
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assert.equal(lastYield, 9);
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});
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it('buffered Promise rejections are suppressed while iterating', async function () {
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let lastYield = null;
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const err = new Error('injected');
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const values = (function* () {
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lastYield = 'promise of 0';
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yield new Promise((resolve) => setTimeout(() => resolve(0), 100));
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lastYield = 'rejected Promise';
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yield Promise.reject(err);
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lastYield = 'promise of 2';
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yield Promise.resolve(2);
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})();
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const s = new Stream(values).buffer(3);
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const iter = s[Symbol.iterator]();
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const nextp = iter.next().value;
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assert.equal(lastYield, 'promise of 2');
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assert.equal(await nextp, 0);
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await assert.rejects(iter.next().value, err);
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iter.return();
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});
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it('buffered Promise rejections are unsuppressed when iteration completes', async function () {
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let lastYield = null;
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const err = new Error('injected');
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const values = (function* () {
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lastYield = 'promise of 0';
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yield new Promise((resolve) => setTimeout(() => resolve(0), 100));
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lastYield = 'rejected Promise';
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yield Promise.reject(err);
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lastYield = 'promise of 2';
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yield Promise.resolve(2);
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})();
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const s = new Stream(values).buffer(3);
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const iter = s[Symbol.iterator]();
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assert.equal(await iter.next().value, 0);
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assert.equal(lastYield, 'promise of 2');
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await assertUnhandledRejection(() => iter.return(), err);
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});
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});
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describe('map', function () {
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it('empty', async function () {
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let called = false;
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assert.deepEqual([...new Stream([]).map((v) => called = true)], []);
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assert.equal(called, false);
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});
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it('does not start until needed', async function () {
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let called = false;
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assert.deepEqual([...new Stream([]).map((v) => called = true)], []);
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new Stream((function* () { yield 0; })()).map((v) => called = true);
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assert.equal(called, false);
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});
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it('works', async function () {
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const calls = [];
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assert.deepEqual(
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[...new Stream([0, 1, 2]).map((v) => { calls.push(v); return 2 * v; })], [0, 2, 4]);
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assert.deepEqual(calls, [0, 1, 2]);
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});
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});
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});
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