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JEST
JEST ASSERTS
ASSERTS BEYOND
BEYOND
EQUALS
EQUALS
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ABOUT ME
ABOUT ME
Software craftsperson at
Software craftsperson at Codurance
Codurance
Oriented to software testing (
Oriented to software testing ( )
)
Testable
Testable
@MatheusMarabesi
🐦
@MatheusMarabesi
🐦
marabesi.com
💻
marabesi.com
💻
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AGENDA
📖
AGENDA
📖
1. Background
2. Assertion smells
3. Assertion API
4. Exploring assertions
5. Wrapping up
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This talk is based on my own journey . . .
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Testing (TDD)
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Framework (Jest)
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toEqual
toEqual, usually is the first assertion used
❗
, usually is the first assertion used
❗
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And, it's something like . . .
🤔
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test('assert some value', () => {
const myVar = 'some val'
expect(myVar).toEqual('some val')
✅
})
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test('light is on', () => {
const off = false
expect(off === false).toEqual(true)
✅
})
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test('it has two users', () => {
const users = [
{ name: 'jhon'},
{ name: 'maria' }
]
expect(users.length).toEqual(2)
✅
})
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ASSERTION SMELLS
ASSERTION SMELLS
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WHEN TEST DRIVEN DEVELOPMENT GOES WRONG
WHEN TEST DRIVEN DEVELOPMENT GOES WRONG
By Continuous Delivery
By Continuous Delivery
When Test Driven Development Goes Wrong
When Test Driven Development Goes Wrong
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expect(myVar).equals('some val')
✅
const myVar = 'some val'
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const off = false
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expect(off === false).equals(true)
✅
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const users = [
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{ name: 'jhon'},
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{ name: 'maria' }
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]
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expect(users.length).equals(2)
✅
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expect(off === false).equals(true)
✅
const myVar = 'some val'
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expect(myVar).equals('some val')
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const off = false
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const users = [
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{ name: 'jhon'},
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{ name: 'maria' }
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]
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expect(users.length).equals(2)
✅
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✅
const myVar = 'some val'
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expect(myVar).equals('some val')
✅
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const off = false
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expect(off === false).equals(true)
✅
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const users = [
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{ name: 'jhon'},
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{ name: 'maria' }
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]
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IS THERE A MORE EXPRESSIVE
IS THERE A MORE EXPRESSIVE
WAY?
🤔
WAY?
🤔
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MEETING THE ASSERTION API
MEETING THE ASSERTION API
5️⃣
5️⃣
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Primitive assertions
🧱
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Modifiers
🪣
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Callbacks
📱
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Async
🏹
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Timers
⏰
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Primitive assertions
🧱
Primitive assertions
🧱
Modifiers
🪣
Modifiers
🪣
Callbacks
📱
Callbacks
📱
Async
🏹
Async
🏹
Timers
⏰
Timers
⏰
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PRIMITIVE ASSERTIONS
🧱
PRIMITIVE ASSERTIONS
🧱
test('it returns a number', () => {
const isNumber = number => number
expect(typeof isNumber(2)).toEqual('number')
})
test('it returns a number', () => {
const isNumber = number => number
expect(isNumber(2)).toEqual(
expect.any(Number)
)
})
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test('expected is greater than the desired', () => {
const expected = 10
const actual = 3
expect(expected > actual).toEqual(true)
})
test('expected is greater than the desired', () => {
const expected = 10
const actual = 3
expect(actual).toBeGreaterThan(expected)
})
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ARRAYS
🧱
ARRAYS
🧱
test('list three fruits', () => {
const expectedFruits = ['banana', 'mango', 'watermelon']
expect(expectedFruits[0]).toEqual('banana')
expect(expectedFruits[1]).toEqual('mango')
expect(expectedFruits[2]).toEqual('watermalo')
})
test('list three fruits', () => {
const expectedFruits = ['banana', 'mango', 'watermelon']
const actualFruits = () => ['banana', 'mango', 'watermelon']
expect(expectedFruits).toEqual(
expect.arrayContaining(actualFruits)
)
})
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test('list with three numbers', () => {
const myList = [1, 2, 3]
expect(myList.length).toEqual(3)
})
test('list with three numbers', () => {
const myList = [1, 2, 3]
expect(myList).toHaveLength(3)
})
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MODIFIERS
🪣
MODIFIERS
🪣
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test('light is on', () => {
const isOff = false
expect(!isOff).toBe(true)
})
test('light is on', () => {
const isOff = false
expect(isOff).not.toBe(true)
})
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CALLBACKS
📱
CALLBACKS
📱
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test('callback has been invoked', done => {
callAsyncFunc(() => {
expect(true).toEqual(true)
done()
})
})
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test('callback has been invoked', () => {
const result = jest.fn()
callAsyncFunc(result)
expect(result).toHaveBeenCalled()
})
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ASYNC
🏹
ASYNC
🏹
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test('my async test', done => {
callAsyncFunc().
then((value) => {
expect(value).toBe(true)
done()
})
})
test('my async test', async () => {
await expect(callAsyncFunc()).resolves.toEqual(true)
})
test('my async test', async () => {
await expect(callAsyncFunc()).rejects.toEqual(false)
})
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TIMERS
⏰
TIMERS
⏰
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Eradicating Non-Determinism in Tests - Asynchronous Behavior
Eradicating Non-Determinism in Tests - Asynchronous Behavior
Martin Fowler, 2011
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function callAsyncFunction() {
return setTimeout(() => {
return Promise.resolve(true)
}, 1000)
}
test('assert after some time', done => {
callAsyncFunc().
then((value) => {
expect(value).toBe(true)
done()
})
})
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describe('using fake timers', () => {
beforeEach(() => {
jest.useFakeTimers()
})
afterEach(() => {
jest.restoreAllMocks()
})
})
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test('should handle next scene', () => {
const value = callAsyncFunc()
jest.advanceTimersByTime(2000);
expect(value).toBe(true)
})
function callAsyncFunction() {
return setTimeout(() => {
return Promise.resolve(true)
}, 1000)
}
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Timer mocks
Timer mocks
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WRAPPING UP
📔
WRAPPING UP
📔
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toEqual
toEqual is usually used more than any assertion
is usually used more than any assertion
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Using different assertions can improve
Using different assertions can improve understading
understading
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HAPPY TESTING
🤪
HAPPY TESTING
🤪
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Talk inspired by:
Talk inspired by:
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3.
4.
Martin Fowler, Eradicating Non-Determinism in Tests (2011)
jest extended
Jest asserts beyond equals (2021)
Jest timers and reactjs (2021)
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ABOUT ME
ABOUT ME
Software craftsperson at
Software craftsperson at
Oriented to software testing (
Oriented to software testing ( )
)
Codurance
Codurance
Testable
Testable
@MatheusMarabesi
🐦
@MatheusMarabesi
🐦
marabesi.com
💻
marabesi.com
💻
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