API Reference
The following types are used in the type signatures below
type DoneCallback = (error?: any) => void
type Awaitable<T> = T | PromiseLike<T>
type TestFunction = () => Awaitable<void> | ((done: DoneCallback) => void)
When a test function returns a promise, the runner will wait until it is resolved to collect async expectations. If the promise is rejected, the test will fail.
For compatibility with Jest, TestFunction
can also be of type (done: DoneCallback) => void
. If this form is used, the test will not be concluded until done
is called (with zero arguments or a falsy value for a successful test, and with a truthy error value as argument to trigger a fail). We don't recommend using this form, as you can achieve the same using an async
function.
test
Type:
(name: string, fn: TestFunction, timeout?: number) => void
Alias:
it
test
defines a set of related expectations. It receives the test name and a function that holds the expectations to test.Optionally, you can provide a timeout (in milliseconds) for specifying how long to wait before terminating. The default is 5 seconds, and can be configured globally with testTimeout
import { expect, test } from 'vitest' test('should work as expected', () => { expect(Math.sqrt(4)).toBe(2) })
test.skip
Type:
(name: string, fn: TestFunction, timeout?: number) => void
Alias:
it.skip
If you want to skip running certain tests, but you don't want to delete the code due to any reason, you can use
test.skip
to avoid running them.import { assert, test } from 'vitest' test.skip('skipped test', () => { // Test skipped, no error assert.equal(Math.sqrt(4), 3) })
test.only
Type:
(name: string, fn: TestFunction, timeout?: number) => void
Alias:
it.only
Use
test.only
to only run certain tests in a given suite. This is useful when debugging.Optionally, you can provide a timeout (in milliseconds) for specifying how long to wait before terminating. The default is 5 seconds, and can be configured globally with testTimeout.
import { assert, test } from 'vitest' test.only('test', () => { // Only this test (and others marked with only) are run assert.equal(Math.sqrt(4), 2) })
test.concurrent
Type:
(name: string, fn: TestFunction, timeout?: number) => void
Alias:
it.concurrent
test.concurrent
marks consecutive tests to be run them in parallel. It receives the test name, an async function with the tests to collect, and an optional timeout (in milliseconds).import { describe, test } from 'vitest' // The two tests marked with concurrent will be run in parallel describe('suite', () => { test('serial test', async() => { /* ... */ }) test.concurrent('concurrent test 1', async() => { /* ... */ }) test.concurrent('concurrent test 2', async() => { /* ... */ }) })
test.skip
,test.only
, andtest.todo
works with concurrent tests. All the following combinations are valid:test.concurrent(/* ... */) test.skip.concurrent(/* ... */) // or test.concurrent.skip(/* ... */) test.only.concurrent(/* ... */) // or test.concurrent.only(/* ... */) test.todo.concurrent(/* ... */) // or test.concurrent.todo(/* ... */)
test.todo
Type:
(name: string) => void
Alias:
it.todo
Use
test.todo
to stub tests to be implemented later. An entry will be shown in the report for the tests so you know how many tests you still need to implement.// An entry will be shown in the report for this test test.todo('unimplemented test')
test.fails
Type:
(name: string, fn: TestFunction, timeout?: number) => void
Alias:
it.fails
Use
test.fails
to indicate that an assertion will fail explicitly.import { expect, test } from 'vitest' const myAsyncFunc = () => new Promise(resolve => resolve(1)) test.fails('fail test', () => { expect(myAsyncFunc()).rejects.toBe(1) })
test.each
Type:
(cases: ReadonlyArray<T>) => void
Alias:
it.each
Use
test.each
when you need to run the same test with different variables. You can inject parameters with printf formmatting in the test name in the order of the test function parameters.%s
: string%d
: number%i
: integer%f
: floating point value%j
: json$o
: object%#
: index of the test case%%
: single precent sign ('%')
test.each([ [1, 1, 2], [1, 2, 3], [2, 1, 3], ])('add(%i, %i) -> %i', (a, b, expected) => { expect(a + b).toBe(expected) }) // this will return // √ add(1, 1) -> 2 // √ add(1, 2) -> 3 // √ add(2, 1) -> 3
describe
When you use test
in the top level of file, they are collected as part of the implicit suite for it. Using describe
you can define a new suite in the current context, as a set of related tests and other nested suites. A suite lets you organize your tests so reports are more clear.
import { describe, expect, test } from 'vitest'
const person = {
isActive: true,
age: 32,
}
describe('person', () => {
test('person is defined', () => {
expect(person).toBeDefined()
})
test('is active', () => {
expect(person.isActive).toBeTruthy()
})
test('age limit', () => {
expect(person.age).toBeLessThanOrEqual(32)
})
})
You can also nest describe blocks if you have a hierarchy of tests:
import { describe, expect, test } from 'vitest'
const numberToCurrency = (value) => {
if (typeof value !== 'number')
throw new Error('Value must be a number')
return value.toFixed(2).toString().replace(/\B(?=(\d{3})+(?!\d))/g, ',')
}
describe('numberToCurrency', () => {
describe('given an invalid number', () => {
test('composed of non-numbers to throw error', () => {
expect(() => numberToCurrency('abc')).toThrow()
})
})
describe('given a valid number', () => {
test('returns the correct currency format', () => {
expect(numberToCurrency(10000)).toBe('10,000.00')
})
})
})
describe.skip
Type:
(name: string, fn: TestFunction) => void
Use
describe.skip
in a suite to avoid running a particular describe block.import { assert, describe, test } from 'vitest' describe.skip('skipped suite', () => { test('sqrt', () => { // Suite skipped, no error assert.equal(Math.sqrt(4), 3) }) })
describe.only
Type:
(name: string, fn: TestFunction) => void
Use
describe.only
to only run certain suites// Only this suite (and others marked with only) are run describe.only('suite', () => { test('sqrt', () => { assert.equal(Math.sqrt(4), 3) }) }) describe('other suite', () => { // ... will be skipped })
describe.concurrent
Type:
(name: string, fn: TestFunction, timeout?: number) => void
describe.concurrent
in a suite marks every tests as concurrent// All tests within this suite will be run in parallel describe.concurrent('suite', () => { test('concurrent test 1', async() => { /* ... */ }) test('concurrent test 2', async() => { /* ... */ }) test.concurrent('concurrent test 3', async() => { /* ... */ }) })
.skip
,.only
, and.todo
works with concurrent suites. All the following combinations are valid:describe.concurrent(/* ... */) describe.skip.concurrent(/* ... */) // or describe.concurrent.skip(/* ... */) describe.only.concurrent(/* ... */) // or describe.concurrent.only(/* ... */) describe.todo.concurrent(/* ... */) // or describe.concurrent.todo(/* ... */)
describe.todo
Type:
(name: string) => void
Use
describe.todo
to stub suites to be implemented later. An entry will be shown in the report for the tests so you know how many tests you still need to implement.// An entry will be shown in the report for this suite describe.todo('unimplemented suite')
describe.each
Type:
(cases: ReadonlyArray<T>): (name: string, fn: (...args: T[]) => void) => void
Use
describe.each
if you have more than one test that depends on the same data.describe.each([ { a: 1, b: 1, expected: 2 }, { a: 1, b: 2, expected: 3 }, { a: 2, b: 1, expected: 3 }, ])('describe object add(%i, %i)', ({ a, b, expected }) => { test(`returns ${expected}`, () => { expect(a + b).toBe(expected) }) test(`returned value not be greater than ${expected}`, () => { expect(a + b).not.toBeGreaterThan(expected) }) test(`returned value not be less than ${expected}`, () => { expect(a + b).not.toBeLessThan(expected) }) })
expect
Type:
ExpectStatic & (actual: any) => Assertions
expect
is used to create assertions. In this contextassertions
are functions that can be called to assert a statement. Vitest provideschai
assertions by default and alsoJest
compatible assertions build on top ofchai
.For example, this code asserts that an
input
value is equal to2
. If it's not, assertion will throw an error, and the test will fail.import { expect } from 'vitest' const input = Math.sqrt(4) expect(input).to.equal(2) // chai API expect(input).toBe(2) // jest API
Technically this example doesn't use
test
function, so in the console you will see Nodejs error instead of Vitest output. To learn more abouttest
, please read next chapter.Also,
expect
can be used statically to access matchers functions, described later, and more.
not
Using not
will negate the assertion. For example, this code asserts that an input
value is not equal to 2
. If it's equal, assertion will throw an error, and the test will fail.
import { expect, test } from 'vitest'
const input = Math.sqrt(16)
expect(input).not.to.equal(2) // chai API
expect(input).not.toBe(2) // jest API
toBe
Type:
(value: any) => Awaitable<void>
toBe
can be used to assert if primitives are equal or that objects share the same reference. It is equivalent of callingexpect(Object.is(3, 3)).toBe(true)
. If the objects are not the same, but you want check if their structures are identical, you can usetoEqual
.For example, the code below checks if the trader has 13 apples.
import { expect, test } from 'vitest' const stock = { type: 'apples', count: 13, } test('stock has 13 apples', () => { expect(stock.type).toBe('apples') expect(stock.count).toBe(13) }) test('stocks are the same', () => { const refStock = stock // same reference expect(stock).toBe(refStock) })
Try not to use
toBe
with floating-point numbers. Since JavaScript rounds them,0.1 + 0.2
is not strictly0.3
. To reliably assert floating-point numbers, usetoBeCloseTo
assertion.
toBeCloseTo
Type:
(value: number, numDigits?: number) => Awaitable<void>
Use
toBeCloseTo
to compare floating-point numbers. The optionalnumDigits
argument limits the number of digits to check after the decimal point. For example:import { expect, test } from 'vitest' test.fails('decimals are not equal in javascript', () => { expect(0.2 + 0.1).toBe(0.3) // 0.2 + 0.1 is 0.30000000000000004 }) test('decimals are rounded to 5 after the point', () => { // 0.2 + 0.1 is 0.30000 | "000000000004" removed expect(0.2 + 0.1).toBeCloseTo(0.3, 5) // nothing from 0.30000000000000004 is removed expect(0.2 + 0.1).not.toBeCloseTo(0.3, 50) })
toBeDefined
Type:
() => Awaitable<void>
toBeDefined
asserts that the value is not equal toundefined
. Useful use case would be to check if function returned anything.import { expect, test } from 'vitest' const getApples = () => 3 test('function returned something', () => { expect(getApples()).toBeDefined() })
toBeUndefined
Type:
() => Awaitable<void>
Opposite of
toBeDefined
,toBeUndefined
asserts that the value is equal toundefined
. Useful use case would be to check if function hasn't returned anything.import { expect, test } from 'vitest' function getApplesFromStock(stock) { if (stock === 'Bill') return 13 } test('mary doesn\'t have a stock', () => { expect(getApplesFromStock('Mary')).toBeUndefined() })
toBeTruthy
Type:
() => Awaitable<void>
toBeTruthy
asserts that the value is true, when converted to boolean. Useful if you don't care for the value, but just want to know it can be converted totrue
.For example having this code you don't care for the return value of
stocks.getInfo
- it maybe complex object, a string or anything else. The code will still work.import { Stocks } from './stocks' const stocks = new Stocks() stocks.sync('Bill') if (stocks.getInfo('Bill')) stocks.sell('apples', 'Bill')
So if you want to test that
stocks.getInfo
will be truthy, you could write:import { expect, test } from 'vitest' import { Stocks } from './stocks' const stocks = new Stocks() test('if we know Bill stock, sell apples to him', () => { stocks.sync('Bill') expect(stocks.getInfo('Bill')).toBeTruthy() })
Everything in JavaScript is truthy, except
false
,0
,''
,null
,undefined
, andNaN
.
toBeFalsy
Type:
() => Awaitable<void>
toBeFalsy
asserts that the value is false, when converted to boolean. Useful if you don't care for the value, but just want to know it can be converted tofalse
.For example having this code you don't care for the return value of
stocks.stockFailed
- it may return any falsy value, but the code will still work.import { Stocks } from './stocks' const stocks = new Stocks() stocks.sync('Bill') if (!stocks.stockFailed('Bill')) stocks.sell('apples', 'Bill')
So if you want to test that
stocks.stockFailed
will be falsy, you could write:import { expect, test } from 'vitest' import { Stocks } from './stocks' const stocks = new Stocks() test('if Bill stock hasnt failed, sell apples to him', () => { stocks.syncStocks('Bill') expect(stocks.stockFailed('Bill')).toBeFalsy() })
Everything in JavaScript is truthy, except
false
,0
,''
,null
,undefined
, andNaN
.
toBeNull
Type:
() => Awaitable<void>
toBeNull
simply asserts if something isnull
. Alias for.toBe(null)
.import { expect, test } from 'vitest' function apples() { return null } test('we dont have apples', () => { expect(apples()).toBeNull() })
toBeNaN
Type:
() => Awaitable<void>
toBeNaN
simply asserts if something isNaN
. Alias for.toBe(NaN)
.import { expect, test } from 'vitest' let i = 0 function getApplesCount() { i++ return i > 1 ? NaN : i } test('getApplesCount has some unusual side effects...', () => { expect(getApplesCount()).not.toBeNaN() expect(getApplesCount()).toBeNaN() })
toBeTypeOf
Type:
(c: 'bigint' | 'boolean' | 'function' | 'number' | 'object' | 'string' | 'symbol' | 'undefined') => Awaitable<void>
toBeTypeOf
asserts if an actual value is of type of received type.import { expect, test } from 'vitest' const actual = 'stock' test('stock is type of string', () => { expect(actual).toBeTypeOf('string') })
toBeInstanceOf
Type:
(c: any) => Awaitable<void>
toBeInstanceOf
asserts if an actual value is instance of received class.import { expect, test } from 'vitest' import { Stocks } from './stocks' const stocks = new Stocks() test('stocks are instance of Stocks', () => { expect(stocks).toBeInstanceOf(Stocks) })
toBeGreaterThan
Type:
(n: number | bigint) => Awaitable<void>
toBeGreaterThan
asserts if actual value is greater than received one. Equal values will fail the test.import { expect, test } from 'vitest' import { getApples } from './stock' test('have more then 10 apples', () => { expect(getApples()).toBeGreaterThan(10) })
toBeGreaterThanOrEqual
Type:
(n: number | bigint) => Awaitable<void>
toBeGreaterThanOrEqual
asserts if actual value is greater than received one or equal to it.import { expect, test } from 'vitest' import { getApples } from './stock' test('have 11 apples or more', () => { expect(getApples()).toBeGreaterThanOrEqual(11) })
toBeLessThan
Type:
(n: number | bigint) => Awaitable<void>
toBeLessThan
asserts if actual value is less than received one. Equal values will fail the test.import { expect, test } from 'vitest' import { getApples } from './stock' test('have less then 20 apples', () => { expect(getApples()).toBeLessThan(20) })
toBeLessThanOrEqual
Type:
(n: number | bigint) => Awaitable<void>
toBeLessThanOrEqual
asserts if actual value is less than received one or equal to it.import { expect, test } from 'vitest' import { getApples } from './stock' test('have 11 apples or less', () => { expect(getApples()).toBeLessThanOrEqual(11) })
toEqual
Type:
(received: any) => Awaitable<void>
toEqual
asserts if actual value is equal to received one or has the same structure, if it is an object (compares them recursively). You can see the difference betweentoEqual
andtoBe
in this example:import { expect, test } from 'vitest' const stockBill = { type: 'apples', count: 13, } const stockMary = { type: 'apples', count: 13, } test('stocks have the same properties', () => { expect(stockBill).toEqual(stockMary) }) test('stocks are not the same', () => { expect(stockBill).not.toBe(stockMary) })
WARNING
A deep equality will not be performed for
Error
objects. To test if something was thrown, usetoThrow
assertion.
toStrictEqual
Type:
(received: any) => Awaitable<void>
toStrictEqual
asserts if actual value is equal to received one or has the same structure, if it is an object (compares them recursively), and of the same type.Differences from
.toEqual
:- Keys with
undefined
properties are checked. e.g.{a: undefined, b: 2}
does not match{b: 2}
when using.toStrictEqual
. - Array sparseness is checked. e.g.
[, 1]
does not match[undefined, 1]
when using.toStrictEqual
. - Object types are checked to be equal. e.g. A class instance with fields
a
andb
will not equal a literal object with fieldsa
andb
.
import { expect, test } from 'vitest' class Stock { constructor(type) { this.type = type } } test('structurally the same, but semantically different', () => { expect(new Stock('apples')).toEqual({ type: 'apples' }) expect(new Stock('apples')).not.toStrictEqual({ type: 'apples' }) })
- Keys with
toContain
Type:
(received: string) => Awaitable<void>
toContain
asserts if actual value is in an array.toContain
can also check whether a string is a substring of another string.import { expect, test } from 'vitest' import { getAllFruits } from './stock' test('the fruit list contains orange', () => { expect(getAllFruits()).toContain('orange') })
toContainEqual
Type:
(received: any) => Awaitable<void>
toContainEqual
asserts if an item with a specific structure and values is contained in an array. It works liketoEqual
inside for each element.import { expect, test } from 'vitest' import { getFruitStock } from './stock' test('apple available', () => { expect(getFruitStock()).toContainEqual({ fruit: 'apple', count: 5 }) })
toHaveLength
Type:
(received: number) => Awaitable<void>
toHaveLength
asserts if an object has a.length
property and it is set to a certain numeric value.import { expect, test } from 'vitest' test('toHaveLength', () => { expect('abc').toHaveLength(3) expect([1, 2, 3]).toHaveLength(3) expect('').not.toHaveLength(3) // doesn't have .length of 3 expect({ length: 3 }).toHaveLength(3) })
toHaveProperty
Type:
(key: any, received?: any) => Awaitable<void>
toHaveProperty
asserts if a property at provided referencekey
exists for an object.You can provide an optional value argument also known as deep equality, like the
toEqual
matcher to compare the received property value.import { expect, test } from 'vitest' const invoice = { 'isActive': true, 'P.O': '12345', 'customer': { first_name: 'John', last_name: 'Doe', location: 'China', }, 'total_amount': 5000, 'items': [ { type: 'apples', quantity: 10, }, { type: 'oranges', quantity: 5, }, ], } test('John Doe Invoice', () => { expect(invoice).toHaveProperty('isActive') // assert that the key exists expect(invoice).toHaveProperty('total_amount', 5000) // assert that the key exists and the value is equal expect(invoice).not.toHaveProperty('account') // assert that this key does not exist // Deep referencing using dot notation expect(invoice).toHaveProperty('customer.first_name') expect(invoice).toHaveProperty('customer.last_name', 'Doe') expect(invoice).not.toHaveProperty('customer.location', 'India') // Deep referencing using an array containing the key expect(invoice).toHaveProperty('items[0].type', 'apples') expect(invoice).toHaveProperty('items.0.type', 'apples') // dot notation also works // Wrap your key in an array to avoid the key from being parsed as a deep reference expect(invoice).toHaveProperty(['P.O'], '12345') })
toMatch
Type:
(received: string | regexp) => Awaitable<void>
toMatch
asserts if a string matches a regular expression or a string.import { expect, test } from 'vitest' test('top fruits', () => { expect('top fruits include apple, orange and grape').toMatch(/apple/) expect('applefruits').toMatch('fruit') // toMatch also accepts a string })
toMatchObject
Type:
(received: object | array) => Awaitable<void>
toMatchObject
asserts if an object matches a subset of the properties of an object.You can also pass an array of objects. This is useful if you want to check that two arrays match in their number of elements, as opposed to
arrayContaining
, which allows for extra elements in the received array.import { expect, test } from 'vitest' const johnInvoice = { isActive: true, customer: { first_name: 'John', last_name: 'Doe', location: 'China', }, total_amount: 5000, items: [ { type: 'apples', quantity: 10, }, { type: 'oranges', quantity: 5, }, ], } const johnDetails = { customer: { first_name: 'John', last_name: 'Doe', location: 'China', }, } test('invoice has john personal details', () => { expect(johnInvoice).toMatchObject(johnDetails) }) test('the number of elements must match exactly', () => { // Assert that an array of object matches expect([{ foo: 'bar' }, { baz: 1 }]).toMatchObject([ { foo: 'bar' }, { baz: 1 }, ]) })
toThrowError
Type:
(received: any) => Awaitable<void>
toThrowError
asserts if a function throws an error when it is called.For example, if we want to test that
getFruitStock('pineapples')
throws, we could write:You can provide an optional argument to test that a specific error is thrown:
- regular expression: error message matches the pattern
- string: error message includes the substring
TIP
You must wrap the code in a function, otherwise the error will not be caught, and the assertion will fail.
import { expect, test } from 'vitest' function getFruitStock(type) { if (type === 'pineapples') throw new DiabetesError('Pineapples is not good for people with diabetes') // Do some other stuff } test('throws on pineapples', () => { // Test that the error message says "diabetes" somewhere: these are equivalent expect(() => getFruitStock('pineapples')).toThrowError(/diabetes/) expect(() => getFruitStock('pineapples')).toThrowError('diabetes') // Test the exact error message expect(() => getFruitStock('pineapples')).toThrowError( /^Pineapples is not good for people with diabetes$/, ) })
toHaveBeenCalled
Type:
() => Awaitable<void>
This assertion is useful for testing that a function has been called. Requires a spy function to be passed to
expect
.import { expect, test, vi } from 'vitest' const market = { buy(subject: string, amount: number) { // ... }, } test('spy function', () => { const buySpy = vi.spyOn(market, 'buy') expect(buySpy).not.toHaveBeenCalled() market.buy('apples', 10) expect(buySpy).toHaveBeenCalled() })
toHaveBeenCalledTimes
- Type:
(amount: number) => Awaitable<void>
This assertion checks if a function was called a certain amount of times. Requires a spy function to be passed to expect
.
import { expect, test, vi } from 'vitest'
const market = {
buy(subject: string, amount: number) {
// ...
},
}
test('spy function called two times', () => {
const buySpy = vi.spyOn(market, 'buy')
market.buy('apples', 10)
market.buy('apples', 20)
expect(buySpy).toHaveBeenCalledTimes(2)
})
toHaveBeenCalledWith
- Type:
(...args: any[]) => Awaitable<void>
This assertion checks if a function was called at least once with certain parameters. Requires a spy function to be passed to expect
.
import { expect, test, vi } from 'vitest'
const market = {
buy(subject: string, amount: number) {
// ...
},
}
test('spy function', () => {
const buySpy = vi.spyOn(market, 'buy')
market.buy('apples', 10)
market.buy('apples', 20)
expect(buySpy).toHaveBeenCalledWith('apples', 10)
expect(buySpy).toHaveBeenCalledWith('apples', 20)
})
toHaveBeenLastCalledWith
- Type:
(...args: any[]) => Awaitable<void>
This assertion checks if a function was called with certain parameters at it's last invokation. Requires a spy function to be passed to expect
.
import { expect, test, vi } from 'vitest'
const market = {
buy(subject: string, amount: number) {
// ...
},
}
test('spy function', () => {
const buySpy = vi.spyOn(market, 'buy')
market.buy('apples', 10)
market.buy('apples', 20)
expect(buySpy).not.toHaveBeenLastCalledWith('apples', 10)
expect(buySpy).toHaveBeenLastCalledWith('apples', 20)
})
toHaveBeenNthCalledWith
- Type:
(time: number, ...args: any[]) => Awaitable<void>
This assertion checks if a function was called with certain parameters at the certain time. The count starts at 1. So, to check the second entry, you would write .toHaveBeenNthCalledWith(2, ...)
.
Requires a spy function to be passed to expect
.
import { expect, test, vi } from 'vitest'
const market = {
buy(subject: string, amount: number) {
// ...
},
}
test('first call of spy function called with right params', () => {
const buySpy = vi.spyOn(market, 'buy')
market.buy('apples', 10)
market.buy('apples', 20)
expect(buySpy).toHaveBeenNthCalledWith(1, 'apples', 10)
})
toHaveReturned
- Type:
() => Awaitable<void>
This assertion checks if a function has successfully returned a value at least once (i.e., did not throw an error). Requires a spy function to be passed to expect
.
import { expect, test, vi } from 'vitest'
const getApplesPrice = (amount: number) => {
const PRICE = 10
return amount * PRICE
}
test('spy function returned a value', () => {
const getPriceSpy = vi.fn(getApplesPrice)
const price = getPriceSpy(10)
expect(price).toBe(100)
expect(getPriceSpy).toHaveReturned()
})
toHaveReturnedTimes
- Type:
(amount: number) => Awaitable<void>
This assertion checks if a function has successfully returned a value exact amount of times (i.e., did not throw an error). Requires a spy function to be passed to expect
.
import { expect, test, vi } from 'vitest'
test('spy function returns a value two times', () => {
const sell = vi.fn((product: string) => ({ product }))
sell('apples')
sell('bananas')
expect(sell).toHaveReturnedTimes(2)
})
toHaveReturnedWith
- Type:
(returnValue: any) => Awaitable<void>
You can call this assertion to check if a function has successfully returned a value with certain parameters at least once. Requires a spy function to be passed to expect
.
import { expect, test, vi } from 'vitest'
test('spy function returns a product', () => {
const sell = vi.fn((product: string) => ({ product }))
sell('apples')
expect(sell).toHaveReturnedWith({ procuct: 'apples' })
})
toHaveLastReturnedWith
- Type:
(returnValue: any) => Awaitable<void>
You can call this assertion to check if a function has successfully returned a value with certain parameters on it's last invoking. Requires a spy function to be passed to expect
.
import { expect, test, vi } from 'vitest'
test('spy function returns bananas on a last call', () => {
const sell = vi.fn((product: string) => ({ product }))
sell('apples')
sell('bananas')
expect(sell).toHaveLastReturnedWith({ procuct: 'bananas' })
})
toHaveNthReturnedWith
- Type:
(time: number, returnValue: any) => Awaitable<void>
You can call this assertion to check if a function has successfully returned a value with certain parameters on a certain call. Requires a spy function to be passed to expect
.
import { expect, test, vi } from 'vitest'
test('spy function returns bananas on second call', () => {
const sell = vi.fn((product: string) => ({ product }))
sell('apples')
sell('bananas')
expect(sell).toHaveNthReturnedWith(2, { product: 'bananas' })
})
resolves
Type:
Promisify<Assertions>
resolves
is intended to remove boilerplate when asserting asynchronous code. Use it to unwrap value from pending promise and assert its value with usual assertions. If promise rejects, the assertion will fail.It returns the same
Assertions
object, but all matchers are now returnPromise
, so you would need toawait
it. Also works withchai
assertions.For example, if you have a function, that makes an API call and returns some data, you may use this code to assert its return value:
import { expect, test } from 'vitest' function buyApples() { return fetch('/buy/apples').then(r => r.json()) } test('buyApples returns new stock id', async() => { // toEqual returns a promise now, so you HAVE to await it await expect(buyApples()).resolves.toEqual({ id: 1 }) // jest API await expect(buyApples()).resolves.to.equal({ id: 1 }) // chai API })
WARNING
If the assertion is not awaited, then you will have a false-positive test that will pass every time. To make sure that assertions are actually called, you may use
expect.assertions(number)
.
rejects
Type:
Promisify<Assertions>
rejects
is intended to remove boilerplate when asserting asynchronous code. Use it to unwrap reason why promise was rejected, and assert its value with usual assertions. If promise successfully resolves, the assertion will fail.It returns the same
Assertions
object, but all matchers are now returnPromise
, so you would need toawait
it. Also works withchai
assertions.For example, if you have a function that fails when you call it, you may use this code to assert the reason:
import { expect, test } from 'vitest' function buyApples(id) { if (!id) throw new Error('no id') } test('buyApples throws an error when no id provided', async() => { // toThrow returns a promise now, so you HAVE to await it await expect(buyApples()).rejects.toThrow('no id') })
WARNING
If the assertion is not awaited, then you will have a false-positive test that will pass every time. To make sure that assertions are actually happened, you may use
expect.assertions(number)
.
expect.assertions
Type:
(count: number) => void
After the test has passed or failed verifies that curtain number of assertions was called during a test. Useful case would be to check if an asynchronous code was called.
For examples, if we have a function than asynchronously calls two matchers, we can assert that they were actually called.
import { expect, test } from 'vitest' async function doAsync(...cbs) { await Promise.all( cbs.map((cb, index) => cb({ index })), ) } test('all assertions are called', async() => { expect.assertions(2) function callback1(data) { expect(data).toBeTruthy() } function callback2(data) { expect(data).toBeTruthy() } await doAsync(callback1, callback2) })
expect.hasAssertions
Type:
(count: number) => void
After the test has passed or failed verifies that at least one assertion was called during a test. Useful case would be to check if an asynchronous code was called.
For example, if you have a code that calls a callback, we can make an assertion inside a callback, but the test will always pass, if we don't check if an assertion was called.
import { expect, test } from 'vitest' import { db } from './db' const cbs = [] function onSelect(cb) { cbs.push(cb) } // after selecting from db, we call all callbacks function select(id) { return db.select({ id }).then((data) => { return Promise.all( cbs.map(cb => cb(data)), ) }) } test('callback was called', async() => { expect.hasAssertions() onSelect((data) => { // should be called on select expect(data).toBeTruthy() }) // if not awaited, test will fail // if you dont have expect.hasAssertions(), test will pass await select(3) })
Setup and Teardown
These functions allow you to hook into the life cycle of tests to avoid repeating setup and teardown code. They apply to the current context: the file if they are used at the top-level or the current suite if they are inside a describe
block.
beforeEach
Type:
beforeEach(fn: () => Awaitable<void>, timeout?: number)
Register a callback to be called before each of the tests in the current context runs. If the function returns a promise, Vitest waits until the promise resolve before running the test.
Optionally, you can pass a timeout (in milliseconds) defining how long to wait before terminating. The default is 5 seconds.
import { beforeEach } from 'vitest' beforeEach(async() => { // Clear mocks and add some testing data after before each test run await stopMocking() await addUser({ name: 'John' }) })
Here, the
beforeEach
ensures that user is added for each test.
afterEach
Type:
afterEach(fn: () => Awaitable<void>, timeout?: number)
Register a callback to be called after each one of the tests in the current context completes. If the function returns a promise, Vitest waits until the promise resolve before continuing.
Optionally, you can a timeout (in milliseconds) for specifying how long to wait before terminating. The default is 5 seconds.
import { afterEach } from 'vitest' afterEach(async() => { await clearTestingData() // clear testing data after each test run })
Here, the
afterEach
ensures that testing data is cleared after each test runs.
beforeAll
Type:
beforeAll(fn: () => Awaitable<void>, timeout?: number)
Register a callback to be called once before starting to run all tests in the current context. If the function returns a promise, Vitest waits until the promise resolve before running tests.
Optionally, you can provide a timeout (in milliseconds) for specifying how long to wait before terminating. The default is 5 seconds.
import { beforeAll } from 'vitest' beforeAll(async() => { await startMocking() // called once before all tests run })
Here the
beforeAll
ensures that the mock data is set up before tests run
afterAll
Type:
afterAll(fn: () => Awaitable<void>, timeout?: number)
Register a callback to be called once after all tests have run in the current context. If the function returns a promise, Vitest waits until the promise resolve before continuing.
Optionally, you can provide a timeout (in milliseconds) for specifying how long to wait before terminating. The default is 5 seconds.
import { afterAll } from 'vitest' afterAll(async() => { await stopMocking() // this method is called after all tests run })
Here the
afterAll
ensures thatstopMocking
method is called after all tests run.
Vi
Vitest provides utility functions to help you out through it's vi helper. You can import { vi } from 'vitest'
or access it globally (when globals configuration is enabled).
vi.advanceTimersByTime
Type:
(ms: number) => Vitest
Works just like
runAllTimers
, but will end after passed milliseconds. For example this will log1, 2, 3
and will not throw:let i = 0 setInterval(() => console.log(++i), 50) vi.advanceTimersByTime(150)
vi.advanceTimersToNextTimer
Type:
() => Vitest
Will call next available timer. Useful to make assertions between each timer call. You can chain call it to manage timers by yourself.
let i = 0 setInterval(() => console.log(++i), 50) vi.advanceTimersToNextTimer() // log 1 .advanceTimersToNextTimer() // log 2 .advanceTimersToNextTimer() // log 3
vi.clearAllTimers
Removes all timers that are scheduled to run. These timers will never run in the future.
vi.fn
Type:
(fn: Function) => CallableMockInstance
Creates a spy on a function, though can be initiated without one. Every time a function is invoked, it stores its call arguments, returns and instances. Also, you can manipulate its behavior with methods. If no function is given, mock will return
undefined
, when invoked.const getApples = vi.fn(() => 0) getApples() expect(getApples).toHaveBeenCalled() expect(getApples).toHaveReturnedWith(0) getApples.mockReturnValueOnce(5) const res = getApples() expect(res).toBe(5) expect(getApples).toHaveNthReturnedWith(2, 5)
vi.getMockedSystemTime
Type:
() => Date | null
Returns mocked current date that was set using
setSystemTime
. If date is not mocked, will returnnull
.
vi.getRealSystemTime
Type:
() => number
When using
vi.useFakeTimers
,Date.now
calls are mocked. If you need to get real time in milliseconds, you can call this function.
vi.mock
Type:
(path: string, factory?: () => unknown) => void
Makes all
imports
to passed module to be mocked. Inside a path you can use configured Vite aliases.- If
factory
is defined, will return its result. Factory function can be asynchronous. You may callvi.importActual
inside to get the original module. The call tovi.mock
is hoisted to the top of the file, so you don't have access to variables declared in the global file scope! - If mocking a module with a default export, you'll need to provide a
default
key within the returned factory function object. This is an ES modules specific caveat, thereforejest
documentation may differ asjest
uses commonJS modules. Example:
vi.mock('path', () => { return { default: { myDefaultKey: vi.fn() }, namedExport: vi.fn(), // etc... } })
- If
__mocks__
folder with file of the same name exist, all imports will return its exports. For example,vi.mock('axios')
with<root>/__mocks__/axios.ts
folder will return everything exported fromaxios.ts
. - If there is no
__mocks__
folder or a file with the same name inside, will call original module and mock it. (For the rules applied, see algorithm.)
- If
vi.setSystemTime
Type:
(date: string | number | Date) => void
Sets current date to the one that was passed. All
Date
calls will return this date.Useful if you need to test anything that depends on the current date - for example luxon calls inside your code.
const date = new Date(1998, 11, 19) vi.useFakeTimers() vi.setSystemTime(date) expect(Date.now()).toBe(date.valueOf()) vi.useRealTimers()
vi.mocked
Type:
<T>(obj: T, deep?: boolean) => MaybeMockedDeep<T>
Type helper for TypeScript. In reality just returns the object that was passed.
import example from './example' vi.mock('./example') test('1+1 equals 2', async() => { vi.mocked(example.calc).mockRestore() const res = example.calc(1, '+', 1) expect(res).toBe(2) })
vi.importActual
Type:
<T>(path: string) => Promise<T>
Imports module, bypassing all checks if it should be mocked. Can be useful if you want to mock module partially.
vi.mock('./example', async() => { const axios = await vi.importActual('./example') return { ...axios, get: vi.fn() } })
vi.importMock
Type:
<T>(path: string) => Promise<MaybeMockedDeep<T>>
Imports a module with all of its properties (including nested properties) mocked. Follows the same rules that
vi.mock
follows. For the rules applied, see algorithm.
vi.restoreCurrentDate
Type:
() => void
Restores
Date
back to its native implementation.
vi.runAllTicks
Type:
() => Vitest
Calls every microtask. These are usually queued by
proccess.nextTick
. This will also run all microtasks scheduled by themselves.
vi.runAllTimers
Type:
() => Vitest
This method will invoke every initiated timer until the timers queue is empty. It means that every timer called during
runAllTimers
will be fired. If you have an infinite interval, it will throw after 10 000 tries. For example this will log1, 2, 3
:let i = 0 setTimeout(() => console.log(++i)) const interval = setInterval(() => { console.log(++i) if (i === 2) clearInterval(interval) }, 50) vi.runAllTimers()
vi.runOnlyPendingTimers
Type:
() => Vitest
This method will call every timer that was initiated after
vi.useFakeTimers()
call. It will not fire any timer that was initiated during its call. For example this will only log1
:let i = 0 setInterval(() => console.log(++i), 50) vi.runOnlyPendingTimers()
vi.spyOn
Type:
<T, K extends keyof T>(object: T, method: K, accessType?: 'get' | 'set') => MockInstance
Creates a spy on a method or getter/setter of an object.
let apples = 0 const obj = { getApples: () => 13, } const spy = vi.spyOn(obj, 'getApples').mockImplementation(() => apples) apples = 1 expect(obj.getApples()).toBe(1) expect(spy).toHaveBeenCalled() expect(spy).toHaveReturnedWith(1)
vi.unmock
Type: (path: string) => void
Removes module from mocked registry. All subsequent calls to import will return original module even if it was mocked.
vi.useFakeTimers
Type:
() => Vitest
To enable mocking timers, you need to call this method. It will wrap all further calls to timers (such as
setTimeout
,setInterval
,clearTimeout
,clearInterval
,nextTick
,setImmediate
,clearImmediate
, andDate
), untilvi.useRealTimers()
is called.The implementation is based internally on
@sinonjs/fake-timers
.
vi.useRealTimers
Type:
() => Vitest
When timers are run out, you may call this method to return mocked timers to its original implementations. All timers that were run before will not be restored.
MockInstance Methods
getMockName
Type:
() => string
Use it to return the name given to mock with method
.mockName(name)
.
mockClear
Type:
() => MockInstance
Clears all information about every call. After calling it,
spy.mock.calls
,spy.mock.results
will return empty arrays. It is useful if you need to clean up spy between different assertions.If you want this method to be called before each test automatically, you can enable
clearMocks
setting in config.
mockName
Type:
(name: string) => MockInstance
Sets internal mock name. Useful to see what mock has failed the assertion.
mockImplementation
Type:
(fn: Function) => MockInstance
Accepts a function that will be used as an implementation of the mock.
For example:
const mockFn = vi.fn().mockImplementation(apples => apples + 1) // or: vi.fn(apples => apples + 1); const NelliesBucket = mockFn(0) const BobsBucket = mockFn(1) NelliesBucket === 1 // true BobsBucket === 2 // true mockFn.mock.calls[0][0] === 0 // true mockFn.mock.calls[1][0] === 1 // true
mockImplementationOnce
Type:
(fn: Function) => MockInstance
Accepts a function that will be used as an implementation of the mock for one call to the mocked function. Can be chained so that multiple function calls produce different results.
const myMockFn = vi .fn() .mockImplementationOnce(() => true) .mockImplementationOnce(() => false) myMockFn() // true myMockFn() // false
When the mocked function runs out of implementations, it will invoke the default implementation that was set with
vi.fn(() => defaultValue)
or.mockImplementation(() => defaultValue)
if they were called:const myMockFn = vi .fn(() => 'default') .mockImplementationOnce(() => 'first call') .mockImplementationOnce(() => 'second call') // 'first call', 'second call', 'default', 'default' console.log(myMockFn(), myMockFn(), myMockFn(), myMockFn())
mockRejectedValue
Type:
(value: any) => MockInstance
Accepts an error that will be rejected, when async function will be called.
test('async test', async() => { const asyncMock = vi.fn().mockRejectedValue(new Error('Async error')) await asyncMock() // throws "Async error" })
mockRejectedValueOnce
Type:
(value: any) => MockInstance
Accepts a value that will be rejected for one call to the mock function. If chained, every consecutive call will reject passed value.
test('async test', async() => { const asyncMock = vi .fn() .mockResolvedValueOnce('first call') .mockRejectedValueOnce(new Error('Async error')) await asyncMock() // first call await asyncMock() // throws "Async error" })
mockReset
Type:
() => MockInstance
Does what
mockClear
does and makes inner implementation as an empty function (returningundefined
, when invoked). This is useful when you want to completely reset a mock back to its initial state.If you want this method to be called before each test automatically, you can enable
mockReset
setting in config.
mockRestore
Type:
() => MockInstance
Does what
mockRestore
does and restores inner implementation to the original function.Note that restoring mock from
vi.fn()
will set implementation to an empty function that returnsundefined
. Restoring avi.fn(impl)
will restore implementation toimpl
.If you want this method to be called before each test automatically, you can enable
restoreMocks
setting in config.
mockResolvedValue
Type:
(value: any) => MockInstance
Accepts a value that will be resolved, when async function will be called.
test('async test', async() => { const asyncMock = vi.fn().mockResolvedValue(43) await asyncMock() // 43 })
mockResolvedValueOnce
Type:
(value: any) => MockInstance
Accepts a value that will be resolved for one call to the mock function. If chained, every consecutive call will resolve passed value.
test('async test', async() => { const asyncMock = vi .fn() .mockResolvedValue('default') .mockResolvedValueOnce('first call') .mockResolvedValueOnce('second call') await asyncMock() // first call await asyncMock() // second call await asyncMock() // default await asyncMock() // default })
mockReturnThis
Type:
() => MockInstance
Sets inner implementation to return
this
context.
mockReturnValue
Type:
(value: any) => MockInstance
Accepts a value that will be returned whenever the mock function is called.
const mock = vi.fn() mock.mockReturnValue(42) mock() // 42 mock.mockReturnValue(43) mock() // 43
mockReturnValueOnce
Type:
(value: any) => MockInstance
Accepts a value that will be returned for one call to the mock function. If chained, every consecutive call will return passed value. When there are no more
mockReturnValueOnce
values to use, calls a function specified bymockImplementation
or othermockReturn*
methods.const myMockFn = vi .fn() .mockReturnValue('default') .mockReturnValueOnce('first call') .mockReturnValueOnce('second call') // 'first call', 'second call', 'default', 'default' console.log(myMockFn(), myMockFn(), myMockFn(), myMockFn())
MockInstance Properties
mock.calls
This is an array containing all arguments for each call. One item of the array is arguments of that call.
If a function was invoked twice with the following arguments fn(arg1, arg2)
, fn(arg3, arg4)
in that order, then mock.calls
will be:
[
['arg1', 'arg2'],
['arg3', 'arg4'],
]
mock.results
This is an array containing all values, that were returned
from function. One item of the array is an object with properties type
and value
. Available types are:
'return'
- function returned without throwing.'throw'
- function threw a value.
The value
property contains returned value or thrown error.
If function returned result
, then threw an error, then mock.results
will be:
[
{
type: 'return',
value: 'result',
},
{
type: 'throw',
value: Error,
},
]
mock.instances
Currently, this property is not implemented.