An example of tests of a function with stream and promises

not-so-simple-stream-example.spec.ts

import { expect } from 'chai';
import { stub, SinonStub, match } from 'sinon';
import * as zlib from 'zlib';
import { notSoSimpleStreamExample } from '../src/not-so-simple-stream-example';
import { ObjectReadableMock } from 'stream-mock';

describe('notSoSimpleStreamExample()', () => {
	let data: any[] = [];
	let gzip: SinonStub<any, any>;

	beforeEach(() => {
		data = [];
		gzip = stub(zlib, 'gzip');
	});

	it('should return array with gzipped values when no error occurs', async () => {
		const stream = new ObjectReadableMock(['value1', 'value2', 'value3']);
		gzip.callsFake(((info, callback: zlib.CompressCallback) => {
			callback(null, `gzipped ${info}` as any);
		}));

		const result = await notSoSimpleStreamExample(stream as any);

		expect(zlib.gzip).to.have.been.calledThrice
			.calledWithExactly('value1', match.func)
			.calledWithExactly('value2', match.func)
			.calledWithExactly('value3', match.func);
		expect(result).to.be.eql([
			'gzipped value1',
			'gzipped value2',
			'gzipped value3',
		]);
	});

	it('should throw error when an error on gzip occurs', async () => {
		const stream = new ObjectReadableMock(['value1', 'value2', 'value3']);
		const myError = new Error('Some nasty error');
		gzip.throws(myError);
		let thrownError: any;

		try {
			await notSoSimpleStreamExample(stream as any);
		} catch (error) {
			thrownError = error;
		}

		expect(zlib.gzip).to.have.been.calledThrice
			.calledWithExactly('value1', match.func)
			.calledWithExactly('value2', match.func)
			.calledWithExactly('value3', match.func);
		expect(thrownError).to.be.eq(myError);
	});
});