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ASSERTIONS
codurance.com
Improving testing
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Matheus Marabesi
Hello there, you can call me Marabesi,
But my name is Matheus Marabesi, I work at Codurance as a
Software craftsperson.
I enjoy talking about anything related to: testing, patterns and
gamification.
You can find me at @MatheusMarabesi or https://marabesi.com
Codurance
Crafting Code
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1. Intro - Background
2. Assertion smells
3. Assertion API
4. Exploring assertions
5. Wrapping up
Crafting code
Agenda
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1. Intro - Background
2. Assertion smells
3. Assertion API - Jest
4. Exploring assertions
5. Wrapping up
Crafting code
Agenda
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1. Background
Warming up
Getting started
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JOURNEY
This talk is based on my own
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TDD
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https://app.livestorm.co/codurance/testing-anti-patterns-workshop
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Jest - Framework
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Jest - Framework
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ANY - Framework
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ANY - Framework
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toEqual
usually is the first assertion used❗
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🤔
And, it's something like . . .
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Assert
test('assert some value', () => {
const myVar = 'some val'
expect(myVar).toEqual('some val')
})
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Assert
test('assert some value', () => {
const myVar = 'some val'
expect(myVar).toEqual('some val') ✅
})
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Assert
test('light is on', () => {
const off = false
expect(off === false).toEqual(true)
})
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Assert
test('light is on', () => {
const off = false
expect(off === false).toEqual(true) ✅
})
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Assert
test('it has two users', () => {
const users = [
{ name: 'jhon'},
{ name: 'maria' }
]
expect(users.length).toEqual(2)
})
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Assert
test('it has two users', () => {
const users = [
{ name: 'jhon'},
{ name: 'maria' }
]
expect(users.length).toEqual(2) ✅
})
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2. Assertion smells
Smells are something that developers relate to,
has some insight that it's not the best approach
and still can't figure out what.
Crafting code
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Assertion smells
const myVar = 'some val'
expect(myVar).equals('some val') ✅
const off = false
expect(off === false).equals(true) ✅
const users = [
{ name: 'jhon'},
{ name: 'maria' }
]
expect(users.length).equals(2) ✅
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Assertion smells
const myVar = 'some val'
expect(myVar).equals('some val') ✅
const off = false
expect(off === false).equals(true) ✅
const users = [
{ name: 'jhon'},
{ name: 'maria' }
]
expect(users.length).equals(2) ✅
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Assertion smells
const myVar = 'some val'
expect(myVar).equals('some val') ✅
const off = false
expect(off === false).equals(true) ✅
const users = [
{ name: 'jhon'},
{ name: 'maria' }
]
expect(users.length).equals(2) ✅
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Assertion smells
const myVar = 'some val'
expect(myVar).equals('some val') ✅
const off = false
expect(off === false).equals(true) ✅
const users = [
{ name: 'jhon'},
{ name: 'maria' }
]
expect(users.length).equals(2) ✅
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Assertion smells
const myVar = 'some val'
expect(myVar).equals('some val') ✅
const off = false
expect(off === false).equals(true) ✅
const users = [
{ name: 'jhon'},
{ name: 'maria' }
]
expect(users.length).equals(2) ✅
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When Test Driven Development Goes Wrong
Dave Farley - by Continuous Delivery
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A more expressive way? 🤔
IS THERE
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3. Assertion API 5⃣
Meeting the jest assertion API
Crafting code
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Primitive assertions 🧱
Crafting code
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Modifiers 🪣
Crafting code
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Callbacks 📱
Crafting code
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Timers ⏰
Crafting code
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Async 🏹
Crafting code
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Primitive assertions 🧱
Modifiers 🪣
Callbacks 📱
Timers ⏰
Async 🏹
Crafting code
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4. Exploring assertions
Primitive, modifier, callback, timer and
async.
Crafting code
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Primitive assertions 🧱
Numbers, Booleans and Arrays
Crafting code
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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))
})
Numbers
🧱
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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))
})
Numbers
🧱
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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))
})
Numbers
🧱
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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))
})
Numbers
🧱
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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(expected).toBeGreaterThan(actual)
})
Booleans
🧱
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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(expected).toBeGreaterThan(actual)
})
Booleans
🧱
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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(expected).toBeGreaterThan(actual)
})
Booleans
🧱
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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(expected).toBeGreaterThan(actual)
})
Booleans
🧱
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test('list three fruits', () => {
const expectedFruits = ['banana', 'mango', 'watermelon']
expect(expectedFruits[0]).toEqual('banana')
expect(expectedFruits[1]).toEqual('mango')
expect(expectedFruits[2]).toEqual('watermelon')
})
test('list three fruits', () => {
const expectedFruits = ['banana', 'mango', 'watermelon']
const actualFruits = ['banana', 'mango', 'watermelon']
expect(expectedFruits).toEqual(
expect.arrayContaining(actualFruits)
)
})
Arrays
🧱
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test('list three fruits', () => {
const expectedFruits = ['banana', 'mango', 'watermelon']
expect(expectedFruits[0]).toEqual('banana')
expect(expectedFruits[1]).toEqual('mango')
expect(expectedFruits[2]).toEqual('watermelon')
})
test('list three fruits', () => {
const expectedFruits = ['banana', 'mango', 'watermelon']
const actualFruits = ['banana', 'mango', 'watermelon']
expect(expectedFruits).toEqual(
expect.arrayContaining(actualFruits)
)
})
Arrays
🧱
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test('list three fruits', () => {
const expectedFruits = ['banana', 'mango', 'watermelon']
expect(expectedFruits[0]).toEqual('banana')
expect(expectedFruits[1]).toEqual('mango')
expect(expectedFruits[2]).toEqual('watermelon')
})
test('list three fruits', () => {
const expectedFruits = ['banana', 'mango', 'watermelon']
const actualFruits = ['banana', 'mango', 'watermelon']
expect(expectedFruits).toEqual(
expect.arrayContaining(actualFruits)
)
})
Arrays
🧱
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test('list three fruits', () => {
const expectedFruits = ['banana', 'mango', 'watermelon']
expect(expectedFruits[0]).toEqual('banana')
expect(expectedFruits[1]).toEqual('mango')
expect(expectedFruits[2]).toEqual('watermelon')
})
test('list three fruits', () => {
const expectedFruits = ['banana', 'mango', 'watermelon']
const actualFruits = ['banana', 'mango', 'watermelon']
expect(expectedFruits).toEqual(
expect.arrayContaining(actualFruits)
)
})
Arrays
🧱
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test('list three fruits', () => {
const expectedFruits = ['banana', 'mango', 'watermelon']
expect(expectedFruits[0]).toEqual('banana')
expect(expectedFruits[1]).toEqual('mango')
expect(expectedFruits[2]).toEqual('watermelon')
})
test('list three fruits', () => {
const expectedFruits = ['banana', 'mango', 'watermelon']
const actualFruits = ['banana', 'mango', 'watermelon']
expect(expectedFruits).toEqual(expect.arrayContaining(actualFruits))
})
Arrays
🧱
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test('list three fruits', () => {
const expectedFruits = ['banana', 'mango', 'watermelon']
expect(expectedFruits[0]).toEqual('banana')
expect(expectedFruits[1]).toEqual('mango')
expect(expectedFruits[2]).toEqual('watermelon')
})
test('list three fruits', () => {
const expectedFruits = ['banana', 'mango', 'watermelon']
const actualFruits = ['banana', 'mango', 'watermelon']
expect(expectedFruits).toEqual(expect.arrayContaining(actualFruits))
})
Arrays
🧱
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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)
})
Arrays
🧱
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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)
})
Arrays
🧱
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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)
})
Arrays
🧱
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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)
})
Arrays
🧱
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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)
})
Arrays
🧱
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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)
})
Arrays
🧱
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Modifiers 🪣
Not
Crafting code
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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)
})
Not
🪣
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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)
})
Not
🪣
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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)
})
Not
🪣
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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)
})
Not
🪣
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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)
})
Not
🪣
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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)
})
Not
🪣
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Not in the document example
Not
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Callbacks 📱
Functions
Crafting code
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test('callback has been invoked', done => {
callAsyncFunc(() => {
expect(true).toEqual(true)
done()
})
})
test('callback has been invoked', () => {
const result = jest.fn()
callAsyncFunc(result)
expect(result).toHaveBeenCalled()
})
Callbacks
📱
const callAsyncFunc = cb => cb();
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test('callback has been invoked', done => {
callAsyncFunc(() => {
expect(true).toEqual(true)
done()
})
})
test('callback has been invoked', () => {
const result = jest.fn()
callAsyncFunc(result)
expect(result).toHaveBeenCalled()
})
Callbacks
📱
const callAsyncFunc = cb => cb();
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test('callback has been invoked', done => {
callAsyncFunc(() => {
expect(true).toEqual(true)
done()
})
})
test('callback has been invoked', () => {
const result = jest.fn()
callAsyncFunc(result)
expect(result).toHaveBeenCalled()
})
Callbacks
📱
const callAsyncFunc = cb => cb();
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test('callback has been invoked', done => {
callAsyncFunc(() => {
expect(true).toEqual(true)
done()
})
})
test('callback has been invoked', () => {
const result = jest.fn()
callAsyncFunc(result)
expect(result).toHaveBeenCalled()
})
Callbacks
📱
const callAsyncFunc = cb => cb();
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test('callback has been invoked', done => {
callAsyncFunc(() => {
expect(true).toEqual(true)
done()
})
})
test('callback has been invoked', () => {
const result = jest.fn()
callAsyncFunc(result)
expect(result).toHaveBeenCalled()
})
Callbacks
📱
const callAsyncFunc = cb => cb();
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test('callback has been invoked', done => {
callAsyncFunc(() => {
expect(true).toEqual(true)
done()
})
})
test('callback has been invoked', () => {
const result = jest.fn()
callAsyncFunc(result)
expect(result).toHaveBeenCalled()
})
Callbacks
📱
const callAsyncFunc = cb => cb();
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test('callback has been invoked', done => {
callAsyncFunc(() => {
expect(true).toEqual(true)
done()
})
})
test('callback has been invoked', () => {
const result = jest.fn()
callAsyncFunc(result)
expect(result).toHaveBeenCalled()
})
Callbacks
📱
const callAsyncFunc = cb => cb();
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Timers ⏰
setTimeout, setInterval, clearTimeout,
clearInterval
Crafting code
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Asynchronous Behavior
Eradicating
Non-Determinism in Tests
Martin Fowler, 2011
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function callAsyncFunction() {
return new Promise((resolve) => {
setTimeout(() => {
resolve(true);
}, 1000);
});
}
test('assert after some time', done => {
callAsyncFunction().
then((value) => {
expect(value).toBe(true)
done()
})
})
Timers
⏰
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function callAsyncFunction() {
return new Promise((resolve) => {
setTimeout(() => {
resolve(true);
}, 1000);
});
}
test('assert after some time', done => {
callAsyncFunc().
then((value) => {
expect(value).toBe(true)
done()
})
})
Timers
⏰
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function callAsyncFunction() {
return new Promise((resolve) => {
setTimeout(() => {
resolve(true);
}, 1000);
});
}
test('assert after some time', done => {
callAsyncFunction().
then((value) => {
expect(value).toBe(true)
done()
})
})
Timers
⏰
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describe('using fake timers', () => {
beforeEach(() => {
jest.useFakeTimers()
})
afterEach(() => {
jest.useRealTimers()
})
})
Timers
⏰
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test("should handle next scene", async () => {
const value = callAsyncFunction();
jest.advanceTimersByTime(2000);
expect(await value).toBe(true);
});
Timers
⏰
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test("should handle next scene", async () => {
const value = callAsyncFunction();
jest.advanceTimersByTime(2000);
expect(await value).toBe(true);
});
Timers
⏰
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test("should handle next scene", async () => {
const value = callAsyncFunction();
jest.advanceTimersByTime(2000);
expect(await value).toBe(true);
});
Timers
⏰
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test("should handle next scene", async () => {
const value = callAsyncFunction();
jest.advanceTimersByTime(2000);
expect(await value).toBe(true);
});
Timers
⏰
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test("should handle next scene", async () => {
const value = callAsyncFunction();
jest.advanceTimersByTime(2000);
expect(await value).toBe(true);
});
Timers
⏰
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test("should handle next scene", async () => {
const value = callAsyncFunction();
jest.advanceTimersByTime(2000);
expect(await value).toBe(true);
});
Timers
⏰
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Async 🏹
Promises
Crafting code
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test('my async test with then', done => {
callAsyncFunction().
then((value) => {
expect(value).toBe(true)
done()
})
})
test('my async test', async () => {
await expect(callAsyncFunction()).resolves.toEqual(true)
})
test('my async test rejects', async () => {
await expect(rejectsAsyncFunction()).rejects.toEqual(false)
})
Promises
🏹
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test('my async test with then', done => {
callAsyncFunction().
then((value) => {
expect(value).toBe(true)
done()
})
})
test('my async test', async () => {
await expect(callAsyncFunction()).resolves.toEqual(true)
})
test('my async test rejects', async () => {
await expect(rejectsAsyncFunction()).rejects.toEqual(false)
})
Promises
🏹
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test('my async test with then', done => {
callAsyncFunction().
then((value) => {
expect(value).toBe(true)
done()
})
})
test('my async test', async () => {
await expect(callAsyncFunction()).resolves.toEqual(true)
})
test('my async test rejects', async () => {
await expect(rejectsAsyncFunction()).rejects.toEqual(false)
})
Promises
🏹
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test('my async test with then', done => {
callAsyncFunction().
then((value) => {
expect(value).toBe(true)
done()
})
})
test('my async test', async () => {
await expect(callAsyncFunction()).resolves.toEqual(true)
})
test('my async test rejects', async () => {
await expect(rejectsAsyncFunction()).rejects.toEqual(false)
})
Promises
🏹
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test('my async test with then', done => {
callAsyncFunction().
then((value) => {
expect(value).toBe(true)
done()
})
})
test('my async test', async () => {
await expect(callAsyncFunction()).resolves.toEqual(true)
})
test('my async test rejects', async () => {
await expect(rejectsAsyncFunction()).rejects.toEqual(false)
})
Promises
🏹
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6. Wrapping up
We are almost done!
Crafting code
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● toEqual is usually used more than any assertion
● Assertion smells
● Using different assertions can improve understanding
● 🧱, 🪣,📱, ⏰, 🏹
What we covered
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What we covered
HAPPY TESTING 🤪
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Matheus Marabesi
Hello there, you can call me Marabesi,
But my name is Matheus Marabesi, I work at Codurance as a
Software craftsperson.
I enjoy talking about anything related to: testing, patterns and
gamification.
You can find me at @MatheusMarabesi or https://marabesi.com
Codurance
Crafting Code