Unit Testing - The Whys, Whens and Hows

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

Transcript of Unit Testing - The Whys, Whens and Hows

Unit Testing

The Whys, Whens and Hows

Ates Goral - Toronto Node.js Meetup - October 11, 2016

Ates Goral

@atesgoral

http://magnetiq.com

http://github.com/atesgoral

http://stackoverflow.com/users/23501/ates-goral

http://myplanet.com

Definition of a unit test

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

Inconsistent definitions

Here’s what’s common:

● Written by developers● Runs fast● Deterministic● Does not tread into integration test territory

Appreciation of unit testing

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.

Good unit tests

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.

Good code

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

Good reasons

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).

Benefits of unit testing

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

Test-environment-first Programming

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.

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.

Basic test environment setup

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)

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

Let’s write our first proper test

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);

});

});

});

});

Implementation and run

src/arithmetic.js:

*** REDACTED ***

npm test

arithmetic

.sum()

when called with two numbers

✓ should return their sum

Opportunistic implementation

src/arithmetic.js:

exports.sum = (a, b) => {

return 4;

};

https://xkcd.com/221/

Who tests the tests?

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.

OH BTW

Selectively running tests with Mocha

mocha --grep <pattern>

npm test -- --grep <pattern>

e.g.

npm test -- --grep arithmetic

Let’s get asynchronous

Timeout implementation

src/timeout.js:

exports.set = (callback, milliseconds) => {

setTimeout(callback, milliseconds);

};

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);

});

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

Flaky tests are evil

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

Deterministic timing

Bring in Sinon

http://sinonjs.org/

npm install --save-dev sinon

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();

});

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;

});

});

});

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.

Definitions of test doubles

Again, some inconsistencies

● Dummy● Fake● Stub● Spy● Mock

http://www.martinfowler.com/bliki/TestDouble.html

https://en.wikipedia.org/wiki/Test_double

Test doubles - dependency injection

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;

Bring in Sinon-Chai

https://github.com/domenic/sinon-chai

npm install --save-dev sinon-chai

const sinonChai = require('sinon-chai');

chai.use(sinonChai);

Account service test

test/testAccountService.js:

describe('AccountService', () => {

let db = null;

let accountService = null;

beforeEach(() => {

db = {

querySync: sinon.stub()

};

accountService = new AccountService(db);

});

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'

});

Promises

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;

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');

Updated account service test

beforeEach(() => {

db = {

query: sinon.stub()

};

accountService = new AccountService(db);

});

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'

});

});

Negative case

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')

);

});

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]);

};

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

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');

});

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

Making the experience better

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);

Updated positive test

return expect(accountService.findById(1))

.to.eventually.deep.equal({

id: 1,

name: 'John Doe'

});

Updated negative test

return expect(accountService.findById(-1))

.to.eventually.be.rejectedWith(Error, 'Account not found');

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' }

Without dependency injection

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();

});

All code so far

https://github.com/atesgoral/hello-test

Clean commit history with 1 commit per example.

Q&A