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asyncgenerators.spec.js

import {strict as assert} from 'assert';

describe('what happens with a value that has been consumed?', () => {
  it('a yielded value is the same as the consumed value', async () => {
    // Arrange
    const yieldedValue = {answer: 42};
    async function* generatorFunction() {
      yield yieldedValue;
    }
    const generator = generatorFunction();
    // Act
    const {value: consumedValue} = await generator.next();
    // Assert
    assert.equal(yieldedValue, consumedValue);
  });
});

describe('whats a diff between yield and return?', () => {
  it('a return always ends the generator', async () => {
    async function* generatorFunction() {
      return;
    }

    const generator = generatorFunction();
    const {done} = await generator.next();
    assert.equal(done, true);
  });
  it('yielding one value doesnt end the generator', async () => {
    async function* generatorFunction() {
      yield 42;
    }

    const generator = generatorFunction();
    const {done} = await generator.next();
    assert.equal(done, false);
  });
  it('the generator ends when the function returns', async () => {
    async function* generatorFunction() {
      yield 42;
    }

    const generator = generatorFunction();
    await generator.next();
    const {done} = await generator.next();
    assert.equal(done, true);
  });
});

describe('is getting the next item async or the item itself?', () => {
  it('an async generator next method returns a promise',  () => {
    async function* generatorFunction() {
    }

    const generator = generatorFunction();
    const result = generator.next();
    assert.equal(result instanceof Promise, true);
  });
});