Unit Testing - The Whys, Whens and Hows

C7f65a2f291636c0bd19920b2b6d525b?s=47 Ates Goral
October 11, 2016

Unit Testing - The Whys, Whens and Hows

C7f65a2f291636c0bd19920b2b6d525b?s=128

Ates Goral

October 11, 2016
Tweet

Transcript

  1. 1.

    Unit Testing The Whys, Whens and Hows Ates Goral -

    Toronto Node.js Meetup - October 11, 2016
  2. 5.

    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
  3. 6.

    Inconsistent definitions Here’s what’s common: • Written by developers •

    Runs fast • Deterministic • Does not tread into integration test territory
  4. 8.

    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.
  5. 10.

    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.
  6. 11.
  7. 12.

    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
  8. 14.

    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).
  9. 16.

    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
  10. 18.

    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.
  11. 19.

    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.
  12. 21.

    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)
  13. 22.

    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
  14. 24.

    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); }); }); }); });
  15. 25.

    Implementation and run src/arithmetic.js: *** REDACTED *** npm test arithmetic

    .sum() when called with two numbers ✓ should return their sum
  16. 28.
  17. 30.

    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.
  18. 31.
  19. 32.

    Selectively running tests with Mocha mocha --grep <pattern> npm test

    -- --grep <pattern> e.g. npm test -- --grep arithmetic
  20. 35.

    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); });
  21. 36.

    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
  22. 38.

    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
  23. 41.

    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(); });
  24. 42.

    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; }); }); });
  25. 43.

    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.
  26. 45.
  27. 46.

    Again, some inconsistencies • Dummy • Fake • Stub •

    Spy • Mock http://www.martinfowler.com/bliki/TestDouble.html https://en.wikipedia.org/wiki/Test_double
  28. 48.

    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;
  29. 50.

    Account service test test/testAccountService.js: describe('AccountService', () => { let db

    = null; let accountService = null; beforeEach(() => { db = { querySync: sinon.stub() }; accountService = new AccountService(db); });
  30. 51.

    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' });
  31. 52.
  32. 53.

    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;
  33. 55.

    Updated account service test beforeEach(() => { db = {

    query: sinon.stub() }; accountService = new AccountService(db); });
  34. 56.

    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' }); });
  35. 58.

    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') ); });
  36. 59.

    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]); };
  37. 60.

    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
  38. 61.

    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'); });
  39. 62.

    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
  40. 64.

    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);
  41. 67.

    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' }
  42. 69.

    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(); });
  43. 71.

    Q&A