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Unit Testing The Whys, Whens and Hows Ates Goral - Toronto Node.js Meetup - October 11, 2016

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Ates Goral @atesgoral http://magnetiq.com http://github.com/atesgoral http://stackoverflow.com/users/23501/ates-goral

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http://myplanet.com

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Definition of a unit test

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What is a unit? ● Smallest bit of code you can test? ● Talking to the actual resource may be OK if it’s stable and fast ● Classic versus mockist styles (Martin Fowler) ● Solitary versus sociable tests (Jay Fields) ● White box versus black box testing ● What’s important is the contract http://martinfowler.com/bliki/UnitTest.html

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Inconsistent definitions Here’s what’s common: ● Written by developers ● Runs fast ● Deterministic ● Does not tread into integration test territory

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Appreciation of unit testing

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You don’t know unit testing until you’ve unit tested There’s a first time for every developer. Some are more lucky than others because they ramp up in an environment that already embraces unit testing. “But can already write flawless code when I’m in the zone.” True. Because you’re actually running unit tests, without realizing, in your mind when you’re in the zone. Try taking a 3 week break and see what happens to those ephemeral unit tests. Turn those tests into unit test code so that they’re repeatable and unforgettable.

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Good unit tests

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Good unit tests ● Are functionally correct. They don’t just exercise code for the sake of exercising code. ● Don’t depend on subsequent tests -- every test runs in its own clean environment, failure of a test doesn’t bring the entire test suite down ● Run fast. You need to be able to run all of your tests as quickly and as frequently as possible. Otherwise, they lose value. ● Are actually run. Automatically. So that you don’t forget to run them. ● Add new unit tests for newly discovered [and fixed] issues.

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Good code

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Good code ● Good code is more unit testable ● It all comes down to good architecture and design ● Planning for unit tests facilitates good code ● Good encapsulation: interfaces with small surfaces, well-defined contracts, non-leaky abstractions ● Keep interdependencies low

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Good reasons

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Why and what are you unit testing? ● Misguided reasons: processes, meeting performance numbers ● Testing just for testing: glue code that doesn’t have any logic, ineffective tests that don’t actually test the functionality ● Testing legacy code that is actually un-unit-testable Be pragmatic. Don’t waste effort. Sometimes unit testing is not the answer (try end-to-end instead).

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Benefits of unit testing

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Benefits of unit testing Benefits beyond finding bugs: ● Better code ● Safety net for refactoring ● Documentation of functionality (especially when in BDD style) ● Prevents code from becoming an untestable entangled mass

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Test-environment-first Programming

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Be test-ready on day one ● Even if you’re not planning to add test yet ● Even if there’s no code worth testing yet ● Prime your environment for future unit tests ● Especially, CI environment setup can be time consuming ● You never know when that moment will come when you have some critical code that needs unit testing Do this. Please.

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Sidenote: At a bare minimum... Even you have no time or energy to write unit tests as you go, prepare a manual test plan, and someone in your team execute them (manually) prior to releases. Bonus: share the effort as a team. Basic smoke tests, checking for end-to-end sanity and regression. Do this. Please.

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Basic test environment setup

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Setting up Mocha - no configuration needed test/testNothing.js: describe('nothing', () => { it('should do nothing', (done) => { done(); }); }); package.json: "scripts": { "test": "mocha" }, https://mochajs.org/ npm install --save-dev mocha npm test nothing ✓ should do nothing 1 passing (8ms)

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Adding Chai test/testExpectation.js: const chai = require('chai'); const expect = chai.expect; describe('2 + 2', () => { it('should equal 4', () => { expect(2 + 2).to.equal(4); }); }); http://chaijs.com/ npm install --save-dev chai npm test 2 + 2 ✓ should equal 4

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Let’s write our first proper test

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The test test/testArithmetic.js: const arithmetic = require('../src/arithmetic'); describe('arithmetic', () => { describe('.sum()', () => { describe('when called with two numbers', () => { it('should return their sum', () => { expect(arithmetic.sum(2, 2)).to.equal(4); }); }); }); });

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Implementation and run src/arithmetic.js: *** REDACTED *** npm test arithmetic .sum() when called with two numbers ✓ should return their sum

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Opportunistic implementation src/arithmetic.js: exports.sum = (a, b) => { return 4; };

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https://xkcd.com/221/

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Who tests the tests?

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Test correctness ● Should not be just exercising code ● Should be functionally correct ● Subject to peer review? I don’t know of any solutions to ensure test correctness.

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OH BTW

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Selectively running tests with Mocha mocha --grep npm test -- --grep e.g. npm test -- --grep arithmetic

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Let’s get asynchronous

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Timeout implementation src/timeout.js: exports.set = (callback, milliseconds) => { setTimeout(callback, milliseconds); };

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Timeout test test/testTimeout.js: it('should call the callback after the delay', (done) => { const start = Date.now(); timeout.set(() => { const elapsed = Date.now() - start; expect(elapsed).to.equal(100); done(); }, 100); });

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Run npm test timeout .set() when called with a callback and a delay 1) should call the callback after the delay Uncaught AssertionError: expected 105 to equal 100 + expected - actual -105 +100

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Flaky tests are evil

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Write deterministic tests that run fast ● Don’t rely on chance ● A less than 100% pass rate is not acceptable ● Don’t waste time with arbitrary delays ● Use the right tools for the [right] job

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Deterministic timing

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Bring in Sinon http://sinonjs.org/ npm install --save-dev sinon

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Use a spy and a fake timer test/testTimeout.js: const sinon = require('sinon'); describe('timeout', () => { let clock = null; beforeEach(() => { clock = sinon.useFakeTimers(); }); afterEach(() => { clock.restore(); });

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Use a spy and a fake timer (continued) describe('.set()', () => { describe('when called with a callback and a delay', () => { it('should call the callback after the delay', () => { const callback = sinon.spy(); timeout.set(callback, 100); clock.tick(100); expect(callback).to.have.been.called; }); }); });

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Run npm test -- --grep timeout timeout .set() when called with a callback and a delay ✓ should call the callback after the delay 100% pass rate.

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Definitions of test doubles

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Again, some inconsistencies ● Dummy ● Fake ● Stub ● Spy ● Mock http://www.martinfowler.com/bliki/TestDouble.html https://en.wikipedia.org/wiki/Test_double

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Test doubles - dependency injection

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Account service that takes DB as a dependency src/accountService.js: function AccountService(db) { this.db = db; } AccountService.prototype.findById = function (accountId, callback) { const results = this.db.querySync('account', { id: accountId }); callback(results[0]); }; module.exports = AccountService;

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Bring in Sinon-Chai https://github.com/domenic/sinon-chai npm install --save-dev sinon-chai const sinonChai = require('sinon-chai'); chai.use(sinonChai);

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Account service test test/testAccountService.js: describe('AccountService', () => { let db = null; let accountService = null; beforeEach(() => { db = { querySync: sinon.stub() }; accountService = new AccountService(db); });

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Account service test (continued) db.querySync.withArgs('account', { id: 1 }).returns([{ id: 1, name: 'John Doe' }]); const callback = sinon.spy(); accountService.findById(1, callback); expect(callback).to.have.been.calledWith({ id: 1, name: 'John Doe' });

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Promises

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DB now uses promises src/accountService.js: function AccountService(db) { this.db = db; } AccountService.prototype.findById = function (accountId, callback) { return this.db .query('account', { id: accountId }) .then((results) => results[0]); }; module.exports = AccountService;

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Bring in sinon-as-promised https://www.npmjs.com/package/sinon-as-promised npm install --save-dev sinon-as-promised const sinonAsPromised = require('sinon-as-promised');

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Updated account service test beforeEach(() => { db = { query: sinon.stub() }; accountService = new AccountService(db); });

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Updated account service test (continued) db.query.withArgs('account', { id: 1 }).resolves([{ id: 1, name: 'John Doe' }]); return accountService.findById(1) .then((account) => { expect(account).to.deep.equal({ id: 1, name: 'John Doe' }); });

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Negative case

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When account not found db.query.withArgs('account', { id: -1 }).rejects( new Error('Account not found') ); return accountService.findById(-1) .catch((error) => { expect(error).to.deep.equal( new Error('Account not found') ); });

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But wait... src/accountService.js: AccountService.prototype.findById = function (accountId, callback) { if (accountId === -1) { return Promise.resolve({ id: -1, name: 'Negative One' }); } return this.db .query('account', { id: accountId }) .then((results) => results[0]); };

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Run npm test -- --grep account AccountService .findById() when called for an existing account ✓ should return a promise resolved with the account when called for a non-existent account ✓ should return a promise rejected with an error

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Need the positive case to fail the test return accountService.findById(-1) .catch((error) => { expect(error).to.deep.equal( new Error('Account not found') ); }) .then(() => { throw new Error('Should not have been resolved'); });

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Run npm test -- --grep account AccountService .findById() when called for an existing account ✓ should return a promise resolved with the account when called for a non-existent account 1) should return a promise rejected with an error

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Making the experience better

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Bring in Chai as Promised http://chaijs.com/plugins/chai-as-promised/ npm install --save-dev chai-as-promised const chaiAsPromised = require('chai-as-promised'); chai.use(chaiAsPromised);

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Updated positive test return expect(accountService.findById(1)) .to.eventually.deep.equal({ id: 1, name: 'John Doe' });

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Updated negative test return expect(accountService.findById(-1)) .to.eventually.be.rejectedWith(Error, 'Account not found');

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Run npm test -- --grep account AccountService .findById() when called for an existing account ✓ should return a promise resolved with the account when called for a non-existent account 1) should return a promise rejected with an error AssertionError: expected promise to be rejected with 'Error' but it was fulfilled with { id: -1, name: 'Negative One' }

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Without dependency injection

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To intercept any module dependency - Mockery https://github.com/mfncooper/mockery npm install --save-dev mockery beforeEach(() => { mockery.enable({ warnOnReplace: false, warnOnUnregistered: false, useCleanCache: true }); mockery.registerMock('./db', db); }); afterEach(() => { mockery.disable(); });

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All code so far https://github.com/atesgoral/hello-test Clean commit history with 1 commit per example.

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Q&A