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module

bun:testThe 'bun:test' module is a fast, built-in test runner that aims for Jest compatibility. Tests are executed with the Bun runtime, providing significantly improved performance over traditional test runners.

Key features include TypeScript and JSX support, lifecycle hooks (beforeAll, beforeEach, afterEach, afterAll), snapshot testing, UI & DOM testing, watch mode, and script pre-loading. The API supports test assertions with expect, test grouping with describe, mocks, and more.

While Bun aims for compatibility with Jest, not everything is implemented yet. Use bun test to automatically discover and run tests matching common patterns like *.test.ts or *.spec.js.

namespace jesttype MockT extends (...args: any[]) => any = (...args: any[]) => any> = JestMock.MockT>Constructs the type of a mock function, e.g. the return type of jest.fn().

type ReplacedT> = JestMock.ReplacedT>Constructs the type of a replaced property.

type SpiedT extends JestMock.ClassLike | (...args: any[]) => any> = JestMock.SpiedT>Constructs the type of a spied class or function.

type SpiedClassT extends JestMock.ClassLike> = JestMock.SpiedClassT>Constructs the type of a spied class.

type SpiedFunctionT extends (...args: any[]) => any> = JestMock.SpiedFunctionT>Constructs the type of a spied function.

type SpiedGetterT> = JestMock.SpiedGetterT>Constructs the type of a spied getter.

type SpiedSetterT> = JestMock.SpiedSetterT>Constructs the type of a spied setter.

function advanceTimersByTime(milliseconds: number): { advanceTimersByTime: (milliseconds: number) => unknown; advanceTimersToNextTimer: () => unknown; clearAllMocks: () => void; clearAllTimers: () => void; fn: (func?: T) => MockT>; getTimerCount: () => number; isFakeTimers: () => boolean; mock: (id: string, factory: () => any) => void | Promisevoid>; resetAllMocks: () => void; restoreAllMocks: () => void; runAllTimers: () => unknown; runOnlyPendingTimers: () => unknown; spyOn: (obj: T, methodOrPropertyValue: K) => MockExtractT[K], (...args: any[]) => any>>; useFakeTimers: (options?: { now: number | Date }) => unknown; useRealTimers: () => unknown };function advanceTimersToNextTimer(): { advanceTimersByTime: (milliseconds: number) => unknown; advanceTimersToNextTimer: () => unknown; clearAllMocks: () => void; clearAllTimers: () => void; fn: (func?: T) => MockT>; getTimerCount: () => number; isFakeTimers: () => boolean; mock: (id: string, factory: () => any) => void | Promisevoid>; resetAllMocks: () => void; restoreAllMocks: () => void; runAllTimers: () => unknown; runOnlyPendingTimers: () => unknown; spyOn: (obj: T, methodOrPropertyValue: K) => MockExtractT[K], (...args: any[]) => any>>; useFakeTimers: (options?: { now: number | Date }) => unknown; useRealTimers: () => unknown };function clearAllMocks(): void;function clearAllTimers(): void;function fnT extends (...args: any[]) => any>(func?: T): MockT>;function getTimerCount(): number;function isFakeTimers(): boolean;function resetAllMocks(): void;function restoreAllMocks(): void;function runAllTimers(): { advanceTimersByTime: (milliseconds: number) => unknown; advanceTimersToNextTimer: () => unknown; clearAllMocks: () => void; clearAllTimers: () => void; fn: (func?: T) => MockT>; getTimerCount: () => number; isFakeTimers: () => boolean; mock: (id: string, factory: () => any) => void | Promisevoid>; resetAllMocks: () => void; restoreAllMocks: () => void; runAllTimers: () => unknown; runOnlyPendingTimers: () => unknown; spyOn: (obj: T, methodOrPropertyValue: K) => MockExtractT[K], (...args: any[]) => any>>; useFakeTimers: (options?: { now: number | Date }) => unknown; useRealTimers: () => unknown };function runOnlyPendingTimers(): { advanceTimersByTime: (milliseconds: number) => unknown; advanceTimersToNextTimer: () => unknown; clearAllMocks: () => void; clearAllTimers: () => void; fn: (func?: T) => MockT>; getTimerCount: () => number; isFakeTimers: () => boolean; mock: (id: string, factory: () => any) => void | Promisevoid>; resetAllMocks: () => void; restoreAllMocks: () => void; runAllTimers: () => unknown; runOnlyPendingTimers: () => unknown; spyOn: (obj: T, methodOrPropertyValue: K) => MockExtractT[K], (...args: any[]) => any>>; useFakeTimers: (options?: { now: number | Date }) => unknown; useRealTimers: () => unknown };function setSystemTime(now?: number | Date): void;function setTimeout(milliseconds: number): void;function spyOnT extends object, K extends string | number | symbol>(obj: T,methodOrPropertyValue: K): MockExtractT[K], (...args: any[]) => any>>;function useFakeTimers(options?: { now: number | Date }): { advanceTimersByTime: (milliseconds: number) => unknown; advanceTimersToNextTimer: () => unknown; clearAllMocks: () => void; clearAllTimers: () => void; fn: (func?: T) => MockT>; getTimerCount: () => number; isFakeTimers: () => boolean; mock: (id: string, factory: () => any) => void | Promisevoid>; resetAllMocks: () => void; restoreAllMocks: () => void; runAllTimers: () => unknown; runOnlyPendingTimers: () => unknown; spyOn: (obj: T, methodOrPropertyValue: K) => MockExtractT[K], (...args: any[]) => any>>; useFakeTimers: (options?: { now: number | Date }) => unknown; useRealTimers: () => unknown };function useRealTimers(): { advanceTimersByTime: (milliseconds: number) => unknown; advanceTimersToNextTimer: () => unknown; clearAllMocks: () => void; clearAllTimers: () => void; fn: (func?: T) => MockT>; getTimerCount: () => number; isFakeTimers: () => boolean; mock: (id: string, factory: () => any) => void | Promisevoid>; resetAllMocks: () => void; restoreAllMocks: () => void; runAllTimers: () => unknown; runOnlyPendingTimers: () => unknown; spyOn: (obj: T, methodOrPropertyValue: K) => MockExtractT[K], (...args: any[]) => any>>; useFakeTimers: (options?: { now: number | Date }) => unknown; useRealTimers: () => unknown };const describe: Describe[]>Describes a group of related tests.

function sum(a, b) { return a + b; } describe("sum()", () => { test("can sum two values", () => { expect(sum(1, 1)).toBe(2); }); }); const expect: ExpectAsserts that a value matches some criteria.

expect(1 + 1).toBe(2); expect([1,2,3]).toContain(2); expect(null).toBeNull(); const expectTypeOf: expectTypeOfconst mock: (Function?: T) => MockT>const test: Test[]>Runs a test.

test("can check if using Bun", () => { expect(Bun).toBeDefined(); }); test("can make a fetch() request", async () => { const response = await fetch("https://example.com/"); expect(response.ok).toBe(true); }); const vi: { advanceTimersByTime: typeof jest.advanceTimersByTime; advanceTimersToNextTimer: typeof jest.advanceTimersToNextTimer; clearAllMocks: typeof jest.clearAllMocks; clearAllTimers: typeof jest.clearAllTimers; fn: typeof jest.fn; getTimerCount: typeof jest.getTimerCount; isFakeTimers: typeof jest.isFakeTimers; mock: typeof mock.module; resetAllMocks: typeof jest.resetAllMocks; restoreAllMocks: typeof jest.restoreAllMocks; runAllTimers: typeof jest.runAllTimers; runOnlyPendingTimers: typeof jest.runOnlyPendingTimers; spyOn: typeof spyOn; useFakeTimers: typeof jest.useFakeTimers; useRealTimers: typeof jest.useRealTimers }Vitest-compatible mocking utilities Provides Vitest-style mocking API for easier migration from Vitest to Bun

const xdescribe: Describe[]>Skips a group of related tests.

This is equivalent to calling describe.skip().

const xtest: Test[]>Skips a test.

This is equivalent to calling test.skip().

function afterAll(fn: () => void | Promiseunknown> | (done: (err?: unknown) => void) => void,options?: HookOptions): void;Runs a function, once, after all the tests.

This is useful for running clean up tasks, like closing a socket or deleting temporary files.

@param fnthe function to run

let database; afterAll(async () => { if (database) { await database.close(); } }); function afterEach(fn: () => void | Promiseunknown> | (done: (err?: unknown) => void) => void,options?: HookOptions): void;Runs a function after each test.

This is useful for running clean up tasks, like closing a socket or deleting temporary files.

@param fnthe function to run

function beforeAll(fn: () => void | Promiseunknown> | (done: (err?: unknown) => void) => void,options?: HookOptions): void;Runs a function, once, before all the tests.

This is useful for running set up tasks, like initializing a global variable or connecting to a database.

If this function throws, tests will not run in this file.

@param fnthe function to run

let database; beforeAll(async () => { database = await connect("localhost"); }); function beforeEach(fn: () => void | Promiseunknown> | (done: (err?: unknown) => void) => void,options?: HookOptions): void;Runs a function before each test.

This is useful for running set up tasks, like initializing a global variable or connecting to a database.

If this function throws, the test will not run.

@param fnthe function to run

function onTestFinished(fn: () => void | Promiseunknown> | (done: (err?: unknown) => void) => void,options?: HookOptions): void;Runs a function after a test finishes, including after all afterEach hooks.

This is useful for cleanup tasks that need to run at the very end of a test, after all other hooks have completed.

Can only be called inside a test, not in describe blocks.

@param fnthe function to run

test("my test", () => { onTestFinished(() => { // This runs after all afterEach hooks console.log("Test finished!"); }); }); function setDefaultTimeout(milliseconds: number): void;Sets the default timeout for all tests in the current file. If a test specifies a timeout, it will override this value. The default timeout is 5000ms (5 seconds).

@param millisecondsthe number of milliseconds for the default timeout

function setSystemTime(now?: number | Date): ThisTypevoid>;Control the system time used by:

Date.now()new Date()Intl.DateTimeFormat().format()In the future, we may add support for more functions, but we haven't done that yet.

@param nowThe time to set the system time to. If not provided, the system time will be reset.

@returnsthis

function spyOnT extends object, K extends string | number | symbol>(obj: T,methodOrPropertyValue: K): MockExtractT[K], (...args: any[]) => any>>;Create a spy on an object property or method

Type definitionsinterface AsymmetricMatchersYou can extend this interface with declaration merging, in order to add type support for custom asymmetric matchers.

// my_modules.d.ts interface MyCustomMatchers { toBeWithinRange(floor: number, ceiling: number): any; } declare module "bun:test" { interface MatchersT> extends MyCustomMatchers {} interface AsymmetricMatchers extends MyCustomMatchers {} } any(constructor: (...args: any[]) => any | new (...args: any[]) => any): any;Matches anything that was created with the given constructor. You can use it inside toEqual or toBeCalledWith instead of a literal value.

function randocall(fn) { return fn(Math.floor(Math.random() * 6 + 1)); } test('randocall calls its callback with a number', () => { const mock = jest.fn(); randocall(mock); expect(mock).toBeCalledWith(expect.any(Number)); }); anything(): any;Matches anything but null or undefined. You can use it inside toEqual or toBeCalledWith instead of a literal value. For example, if you want to check that a mock function is called with a non-null argument:

test('map calls its argument with a non-null argument', () => { const mock = jest.fn(); [1].map(x => mock(x)); expect(mock).toBeCalledWith(expect.anything()); }); arrayContainingE = any>(arr: readonly E[]): any;Matches any array made up entirely of elements in the provided array. You can use it inside toEqual or toBeCalledWith instead of a literal value.

Optionally, you can provide a type for the elements via a generic.

closeTo(num: number,numDigits?: number): any;Useful when comparing floating point numbers in object properties or array item. If you need to compare a number, use .toBeCloseTo instead.

The optional numDigits argument limits the number of digits to check after the decimal point. For the default value 2, the test criterion is Math.abs(expected - received) (that is, 10 ** -2 / 2).

objectContaining(obj: object): any;Matches any object that recursively matches the provided keys. This is often handy in conjunction with other asymmetric matchers.

Optionally, you can provide a type for the object via a generic. This ensures that the object contains the desired structure.

stringContaining(str: string | String): any;Matches any received string that contains the exact expected string

stringMatching(regex: string | String | RegExp): any;Matches any string that contains the exact provided string

interface AsymmetricMatchersBuiltin any(constructor: (...args: any[]) => any | new (...args: any[]) => any): any;Matches anything that was created with the given constructor. You can use it inside toEqual or toBeCalledWith instead of a literal value.

Optionally, you can provide a type for the elements via a generic.

closeTo(num: number,numDigits?: number): any;Useful when comparing floating point numbers in object properties or array item. If you need to compare a number, use .toBeCloseTo instead.

The optional numDigits argument limits the number of digits to check after the decimal point. For the default value 2, the test criterion is Math.abs(expected - received) (that is, 10 ** -2 / 2).

objectContaining(obj: object): any;Matches any object that recursively matches the provided keys. This is often handy in conjunction with other asymmetric matchers.

Optionally, you can provide a type for the object via a generic. This ensures that the object contains the desired structure.

stringContaining(str: string | String): any;Matches any received string that contains the exact expected string

stringMatching(regex: string | String | RegExp): any;Matches any string that contains the exact provided string

interface DescribeT extends Readonlyany[]>>Describes a group of related tests.

function sum(a, b) { return a + b; } describe("sum()", () => { test("can sum two values", () => { expect(sum(1, 1)).toBe(2); }); }); concurrent: DescribeT>Marks this group of tests to be executed concurrently.

only: DescribeT>Skips all other tests, except this group of tests.

serial: DescribeT>Marks this group of tests to be executed serially (one after another), even when the --concurrent flag is used.

skip: DescribeT>Skips this group of tests.

todo: DescribeT>Marks this group of tests as to be written or to be fixed.

eachT extends any[]>(table: readonly T[]): Describe[...T[]]>;eachT>(table: T[]): Describe[T]>;if(condition: boolean): DescribeT>;Runs this group of tests, only if condition is true.

This is the opposite of describe.skipIf().

@param conditionif these tests should run

skipIf(condition: boolean): DescribeT>;Skips this group of tests, if condition is true.

@param conditionif these tests should be skipped

todoIf(condition: boolean): DescribeT>;Marks this group of tests as to be written or to be fixed, if condition is true.

@param conditionif these tests should be skipped

interface ExpectYou can extend this interface with declaration merging, in order to add type support for custom asymmetric matchers.

expect("abc").toEqual(expect.stringContaining("abc")); // will pass expect("abc").toEqual(expect.not.stringContaining("abc")); // will fail rejectsTo: AsymmetricMatchersCreate an asymmetric matcher for a promise rejected value.

expect(Promise.reject("error")).toEqual(expect.rejectsTo.stringContaining("error")); // will pass expect(Promise.resolve("error")).toEqual(expect.rejectsTo.stringContaining("error")); // will fail expect("error").toEqual(expect.rejectsTo.stringContaining("error")); // will fail resolvesTo: AsymmetricMatchersCreate an asymmetric matcher for a promise resolved value.

expect(Promise.resolve("value")).toEqual(expect.resolvesTo.stringContaining("value")); // will pass expect(Promise.reject("value")).toEqual(expect.resolvesTo.stringContaining("value")); // will fail expect("value").toEqual(expect.resolvesTo.stringContaining("value")); // will fail any(constructor: (...args: any[]) => any | new (...args: any[]) => any): any;Matches anything that was created with the given constructor. You can use it inside toEqual or toBeCalledWith instead of a literal value.

Optionally, you can provide a type for the elements via a generic.

assertions(neededAssertions: number): void;Ensures that a specific number of assertions are made

closeTo(num: number,numDigits?: number): any;Useful when comparing floating point numbers in object properties or array item. If you need to compare a number, use .toBeCloseTo instead.

The optional numDigits argument limits the number of digits to check after the decimal point. For the default value 2, the test criterion is Math.abs(expected - received) (that is, 10 ** -2 / 2).

extendM>(matchers: ExpectExtendMatchersM>): void;Register new custom matchers.

@param matchersAn object containing the matchers to register, where each key is the matcher name, and its value the implementation function. The function must satisfy: (actualValue, ...matcherInstantiationArguments) => { pass: true|false, message: () => string }

expect.extend({ toBeWithinRange(actual, min, max) { if (typeof actual !== 'number' || typeof min !== 'number' || typeof max !== 'number') throw new Error('Invalid usage'); const pass = actual >= min && actual max; return { pass: pass, message: () => `expected ${this.utils.printReceived(actual)} ` + (pass ? `not to be`: `to be`) + ` within range ${this.utils.printExpected(`${min} .. ${max}`)}`, }; }, }); test('some test', () => { expect(50).toBeWithinRange(0, 100); // will pass expect(50).toBeWithinRange(100, 200); // will fail expect(50).toBe(expect.toBeWithinRange(0, 100)); // will pass expect(50).toBe(expect.not.toBeWithinRange(100, 200)); // will pass }); hasAssertions(): void;Ensures that an assertion is made

objectContaining(obj: object): any;Matches any object that recursively matches the provided keys. This is often handy in conjunction with other asymmetric matchers.

Optionally, you can provide a type for the object via a generic. This ensures that the object contains the desired structure.

stringContaining(str: string | String): any;Matches any received string that contains the exact expected string

stringMatching(regex: string | String | RegExp): any;Matches any string that contains the exact provided string

unreachable(msg?: string | Error): never;Throw an error if this function is called.

@param msgOptional message to display if the test fails

@returnsnever

import { expect, test } from "bun:test"; test("!!abc!! is not a module", () => { try { require("!!abc!!"); expect.unreachable(); } catch(e) { expect(e.name).not.toBe("UnreachableError"); } }); interface MatcherResult message?: string | () => stringpass: booleaninterface MatchersT = unknown>You can extend this interface with declaration merging, in order to add type support for custom matchers.

expect().fail(); expect().fail("message is optional"); expect().not.fail(); expect().not.fail("hi"); not: Matchersunknown>Negates the result of a subsequent assertion. If you know how to test something, .not lets you test its opposite.

expect(1).not.toBe(0); expect(null).not.toBeNull(); pass: (message?: string) => voidAssertion which passes.

expect().pass(); expect().pass("message is optional"); expect().not.pass(); expect().not.pass("hi"); rejects: Matchersunknown>Expects the value to be a promise that rejects.

expect(Promise.reject("error")).rejects.toBe("error"); resolves: MatchersAwaitedT>>Expects the value to be a promise that resolves.

expect(Promise.resolve(1)).resolves.toBe(1); lastCalledWith(...expected: unknown[]): void;Ensure that a mock function is called with specific arguments for the nth call.

nthCalledWith(n: number,...expected: unknown[]): void;Ensure that a mock function is called with specific arguments for the nth call.

toBe(expected: T): void;Asserts that a value equals what is expected.

For non-primitive values, like objects and arrays, use toEqual() instead.For floating-point numbers, use toBeCloseTo() instead.@param expectedthe expected value

expect(100 + 23).toBe(123); expect("d" + "og").toBe("dog"); expect([123]).toBe([123]); // fail, use toEqual() expect(3 + 0.14).toBe(3.14); // fail, use toBeCloseTo() // TypeScript errors: expect("hello").toBe(3.14); // typescript error + fail expect("hello").toBenumber>(3.14); // no typescript error, but still fails toBeX = T>(expected: NoInferX>): void;toBeArray(): void;Asserts that a value is a array.

expect([1]).toBeArray(); expect(new Array(1)).toBeArray(); expect({}).not.toBeArray(); toBeArrayOfSize(size: number): void;Asserts that a value is a array of a certain length.

expect([]).toBeArrayOfSize(0); expect([1]).toBeArrayOfSize(1); expect(new Array(1)).toBeArrayOfSize(1); expect({}).not.toBeArrayOfSize(0); toBeBoolean(): void;Asserts that a value is a boolean.

expect(true).toBeBoolean(); expect(false).toBeBoolean(); expect(null).not.toBeBoolean(); expect(0).not.toBeBoolean(); toBeCalled(): void;Ensures that a mock function is called an exact number of times.

toBeCalledTimes(expected: number): void;Ensure that a mock function is called with specific arguments.

toBeCalledWith(...expected: unknown[]): void;Ensure that a mock function is called with specific arguments.

toBeCloseTo(expected: number,numDigits?: number): void;Asserts that value is close to the expected by floating point precision.

For example, the following fails because arithmetic on decimal (base 10) values often have rounding errors in limited precision binary (base 2) representation.

@param expectedthe expected value

@param numDigitsthe number of digits to check after the decimal point. Default is 2

expect(0.2 + 0.1).toBe(0.3); // fails Use `toBeCloseTo` to compare floating point numbers for approximate equality. toBeDate(): void;Asserts that a value is a Date object.

To check if a date is valid, use toBeValidDate() instead.

expect(new Date()).toBeDate(); expect(new Date(null)).toBeDate(); expect("2020-03-01").not.toBeDate(); toBeDefined(): void;Asserts that a value is defined. (e.g. is not undefined)

expect(true).toBeDefined(); expect(undefined).toBeDefined(); // fail toBeEmpty(): void;Asserts that a value is empty.

expect("").toBeEmpty(); expect([]).toBeEmpty(); expect({}).toBeEmpty(); expect(new Set()).toBeEmpty(); toBeEmptyObject(): void;Asserts that a value is an empty object.

expect({}).toBeEmptyObject(); expect({ a: 'hello' }).not.toBeEmptyObject(); toBeEven(): void;Asserts that a number is even.

expect(2).toBeEven(); expect(1).not.toBeEven(); toBeFalse(): void;Asserts that a value is false.

expect(false).toBeFalse(); expect(true).not.toBeFalse(); expect(0).not.toBeFalse(); toBeFalsy(): void;Asserts that a value is "falsy".

To assert that a value equals false, use toBe(false) instead.

expect(true).toBeTruthy(); expect(1).toBeTruthy(); expect({}).toBeTruthy(); toBeFinite(): void;Asserts that a value is a number, and is not NaN or Infinity.

expect(1).toBeFinite(); expect(3.14).toBeFinite(); expect(NaN).not.toBeFinite(); expect(Infinity).not.toBeFinite(); toBeFunction(): void;Asserts that a value is a function.

expect(() => {}).toBeFunction(); toBeGreaterThan(expected: number | bigint): void;Asserts that a value is a number and is greater than the expected value.

@param expectedthe expected number

expect(1).toBeGreaterThan(0); expect(3.14).toBeGreaterThan(3); expect(9).toBeGreaterThan(9); // fail toBeGreaterThanOrEqual(expected: number | bigint): void;Asserts that a value is a number and is greater than or equal to the expected value.

@param expectedthe expected number

expect(1).toBeGreaterThanOrEqual(0); expect(3.14).toBeGreaterThanOrEqual(3); expect(9).toBeGreaterThanOrEqual(9); toBeInstanceOf(value: unknown): void;Asserts that the expected value is an instance of value

expect([]).toBeInstanceOf(Array); expect(null).toBeInstanceOf(Array); // fail toBeInteger(): void;Asserts that a value is a number, and is an integer.

expect(1).toBeInteger(); expect(3.14).not.toBeInteger(); expect(NaN).not.toBeInteger(); toBeLessThan(expected: number | bigint): void;Asserts that a value is a number and is less than the expected value.

@param expectedthe expected number

expect(-1).toBeLessThan(0); expect(3).toBeLessThan(3.14); expect(9).toBeLessThan(9); // fail toBeLessThanOrEqual(expected: number | bigint): void;Asserts that a value is a number and is less than or equal to the expected value.

@param expectedthe expected number

expect(-1).toBeLessThanOrEqual(0); expect(3).toBeLessThanOrEqual(3.14); expect(9).toBeLessThanOrEqual(9); toBeNaN(): void;Asserts that a value is NaN.

Same as using Number.isNaN().

expect(NaN).toBeNaN(); expect(Infinity).toBeNaN(); // fail expect("notanumber").toBeNaN(); // fail toBeNegative(): void;Asserts that a value is a negative number.

expect(-3.14).toBeNegative(); expect(1).not.toBeNegative(); expect(NaN).not.toBeNegative(); toBeNil(): void;Asserts that a value is null or undefined.

expect(null).toBeNil(); expect(undefined).toBeNil(); toBeNull(): void;Asserts that a value is null.

expect(null).toBeNull(); expect(undefined).toBeNull(); // fail toBeNumber(): void;Asserts that a value is a number.

expect(1).toBeNumber(); expect(3.14).toBeNumber(); expect(NaN).toBeNumber(); expect(BigInt(1)).not.toBeNumber(); toBeObject(): void;Asserts that a value is an object.

expect({}).toBeObject(); expect("notAnObject").not.toBeObject(); expect(NaN).not.toBeObject(); toBeOdd(): void;Asserts that a number is odd.

expect(1).toBeOdd(); expect(2).not.toBeOdd(); toBeOneOf(expected: IterableT>): void;Asserts that the value is deep equal to an element in the expected array.

The value must be an array or iterable, which includes strings.

@param expectedthe expected value

expect(1).toBeOneOf([1,2,3]); expect("foo").toBeOneOf(["foo", "bar"]); expect(true).toBeOneOf(new Set([true])); toBeOneOfX = T>(expected: NoInferIterableX, any, any>>): void;toBePositive(): void;Asserts that a value is a positive number.

expect(1).toBePositive(); expect(-3.14).not.toBePositive(); expect(NaN).not.toBePositive(); toBeString(): void;Asserts that a value is a string.

expect("foo").toBeString(); expect(new String("bar")).toBeString(); expect(123).not.toBeString(); toBeSymbol(): void;Asserts that a value is a symbol.

expect(Symbol("foo")).toBeSymbol(); expect("foo").not.toBeSymbol(); toBeTrue(): void;Asserts that a value is true.

expect(true).toBeTrue(); expect(false).not.toBeTrue(); expect(1).not.toBeTrue(); toBeTruthy(): void;Asserts that a value is "truthy".

To assert that a value equals true, use toBe(true) instead.

expect(true).toBeTruthy(); expect(1).toBeTruthy(); expect({}).toBeTruthy(); toBeTypeOf(type: 'string' | 'number' | 'bigint' | 'boolean' | 'symbol' | 'undefined' | 'object' | 'function'): void;Asserts that a value matches a specific type.

expect(1).toBeTypeOf("number"); expect("hello").toBeTypeOf("string"); expect([]).not.toBeTypeOf("boolean"); toBeUndefined(): void;Asserts that a value is undefined.

expect(undefined).toBeUndefined(); expect(null).toBeUndefined(); // fail toBeValidDate(): void;Asserts that a value is a valid Date object.

expect(new Date()).toBeValidDate(); expect(new Date(null)).not.toBeValidDate(); expect("2020-03-01").not.toBeValidDate(); toBeWithin(start: number,end: number): void;Asserts that a value is a number between a start and end value.

@param startthe start number (inclusive)

@param endthe end number (exclusive)

toContain(expected: T extends IterableU, any, any> ? U : T): void;Asserts that a value contains what is expected.

The value must be an array or iterable, which includes strings.

@param expectedthe expected value

expect([1, 2, 3]).toContain(1); expect(new Set([true])).toContain(true); expect("hello").toContain("o"); toContainX = T>(expected: NoInferX extends IterableU, any, any> ? U : X>): void;toContainAllKeys(expected: IfNeverThenElsekeyof T, PropertyKey>[]): void;Asserts that an object contains all the provided keys.

The value must be an object

@param expectedthe expected value

expect({ a: 'hello', b: 'world' }).toContainAllKeys(['a','b']); expect({ a: 'hello', b: 'world' }).toContainAllKeys(['b','a']); expect({ 1: 'hello', b: 'world' }).toContainAllKeys([1,'b']); expect({ a: 'hello', b: 'world' }).not.toContainAllKeys(['c']); expect({ a: 'hello', b: 'world' }).not.toContainAllKeys(['a']); toContainAllKeysX = T>(expected: IfNeverThenElseNoInferkeyof X>, PropertyKey>[]): void;toContainAllValues(expected: unknown[]): void;Asserts that an object contain all the provided values.

The value must be an object

@param expectedthe expected value

const o = { a: 'foo', b: 'bar', c: 'baz' }; expect(o).toContainAllValues(['foo', 'bar', 'baz']); expect(o).toContainAllValues(['baz', 'bar', 'foo']); expect(o).not.toContainAllValues(['bar', 'foo']); toContainAnyKeys(expected: IfNeverThenElsekeyof T, PropertyKey>[]): void;Asserts that an object contains at least one of the provided keys. Asserts that an object contains all the provided keys.

The value must be an object

@param expectedthe expected value

expect({ a: 'hello', b: 'world' }).toContainAnyKeys(['a']); expect({ a: 'hello', b: 'world' }).toContainAnyKeys(['b']); expect({ a: 'hello', b: 'world' }).toContainAnyKeys(['b', 'c']); expect({ a: 'hello', b: 'world' }).not.toContainAnyKeys(['c']); toContainAnyKeysX = T>(expected: IfNeverThenElseNoInferkeyof X>, PropertyKey>[]): void;toContainAnyValues(expected: unknown[]): void;Asserts that an object contain any provided value.

The value must be an object

@param expectedthe expected value

const o = { a: 'foo', b: 'bar', c: 'baz' }; expect(o).toContainAnyValues(['qux', 'foo']); expect(o).toContainAnyValues(['qux', 'bar']); expect(o).toContainAnyValues(['qux', 'baz']); expect(o).not.toContainAnyValues(['qux']); toContainEqual(expected: T extends IterableU, any, any> ? U : T): void;Asserts that a value contains and equals what is expected.

This matcher will perform a deep equality check for members of arrays, rather than checking for object identity.

@param expectedthe expected value

expect([{ a: 1 }]).toContainEqual({ a: 1 }); expect([{ a: 1 }]).not.toContainEqual({ a: 2 }); toContainEqualX = T>(expected: NoInferX extends IterableU, any, any> ? U : X>): void;toContainKey(expected: IfNeverThenElsekeyof T, PropertyKey>): void;Asserts that an object contains a key.

The value must be an object

@param expectedthe expected value

expect({ a: 'foo', b: 'bar', c: 'baz' }).toContainKey('a'); expect({ a: 'foo', b: 'bar', c: 'baz' }).toContainKey('b'); expect({ a: 'foo', b: 'bar', c: 'baz' }).toContainKey('c'); expect({ a: 'foo', b: 'bar', c: 'baz' }).not.toContainKey('d'); toContainKeyX = T>(expected: IfNeverThenElseNoInferkeyof X>, PropertyKey>): void;toContainKeys(expected: IfNeverThenElsekeyof T, PropertyKey>[]): void;Asserts that an object contains all the provided keys.

@param expectedthe expected value

expect({ a: 'foo', b: 'bar', c: 'baz' }).toContainKeys(['a', 'b']); expect({ a: 'foo', b: 'bar', c: 'baz' }).toContainKeys(['a', 'b', 'c']); expect({ a: 'foo', b: 'bar', c: 'baz' }).not.toContainKeys(['a', 'b', 'e']); toContainKeysX = T>(expected: IfNeverThenElseNoInferkeyof X>, PropertyKey>[]): void;toContainValue(expected: unknown): void;Asserts that an object contain the provided value.

This method is deep and will look through child properties to find the expected value.

The input value must be an object.

@param expectedthe expected value

const shallow = { hello: "world" }; const deep = { message: shallow }; const deepArray = { message: [shallow] }; const o = { a: "foo", b: [1, "hello", true], c: "baz" }; expect(shallow).toContainValue("world"); expect({ foo: false }).toContainValue(false); expect(deep).toContainValue({ hello: "world" }); expect(deepArray).toContainValue([{ hello: "world" }]); expect(o).toContainValue("foo", "barr"); expect(o).toContainValue([1, "hello", true]); expect(o).not.toContainValue("qux"); // NOT expect(shallow).not.toContainValue("foo"); expect(deep).not.toContainValue({ foo: "bar" }); expect(deepArray).not.toContainValue([{ foo: "bar" }]); toContainValues(expected: unknown[]): void;Asserts that an object contain the provided value.

This is the same as toContainValue, but accepts an array of values instead.

The value must be an object

@param expectedthe expected value

const o = { a: 'foo', b: 'bar', c: 'baz' }; expect(o).toContainValues(['foo']); expect(o).toContainValues(['baz', 'bar']); expect(o).not.toContainValues(['qux', 'foo']); toEndWith(expected: string): void;Asserts that a value ends with a string.

@param expectedthe string to end with

toEqual(expected: T): void;Asserts that a value is deeply equal to what is expected.

@param expectedthe expected value

expect(100 + 23).toBe(123); expect("d" + "og").toBe("dog"); expect([456]).toEqual([456]); expect({ value: 1 }).toEqual({ value: 1 }); toEqualX = T>(expected: NoInferX>): void;toEqualIgnoringWhitespace(expected: string): void;Asserts that a value is equal to the expected string, ignoring any whitespace.

@param expectedthe expected string

expect(" foo ").toEqualIgnoringWhitespace("foo"); expect("bar").toEqualIgnoringWhitespace(" bar "); toHaveBeenCalled(): void;Ensures that a mock function is called.

toHaveBeenCalledTimes(expected: number): void;Ensures that a mock function is called an exact number of times.

toHaveBeenCalledWith(...expected: unknown[]): void;Ensure that a mock function is called with specific arguments.

toHaveBeenLastCalledWith(...expected: unknown[]): void;Ensure that a mock function is called with specific arguments for the last call.

toHaveBeenNthCalledWith(n: number,...expected: unknown[]): void;Ensure that a mock function is called with specific arguments for the nth call.

toHaveLastReturnedWith(expected: unknown): void;Ensures that a mock function has returned a specific value on its last invocation. This matcher uses deep equality, like toEqual(), and supports asymmetric matchers.

toHaveLength(length: number): void;Asserts that a value has a .length property that is equal to the expected length.

@param lengththe expected length

expect([]).toHaveLength(0); expect("hello").toHaveLength(4); toHaveNthReturnedWith(n: number,expected: unknown): void;Ensures that a mock function has returned a specific value on the nth invocation. This matcher uses deep equality, like toEqual(), and supports asymmetric matchers.

@param nThe 1-based index of the function call

@param expectedThe expected return value

toHaveProperty(keyPath: string | number | string | number[],value?: unknown): void;Asserts that a value has a property with the expected name, and value if provided.

@param keyPaththe expected property name or path, or an index

@param valuethe expected property value, if provided

expect(new Set()).toHaveProperty("size"); expect(new Uint8Array()).toHaveProperty("byteLength", 0); expect({ kitchen: { area: 20 }}).toHaveProperty("kitchen.area", 20); expect({ kitchen: { area: 20 }}).toHaveProperty(["kitchen", "area"], 20); toHaveReturned(): void;Ensures that a mock function has returned successfully at least once.

A promise that is unfulfilled will be considered a failure. If the function threw an error, it will be considered a failure.

toHaveReturnedTimes(times: number): void;Ensures that a mock function has returned successfully at times times.

A promise that is unfulfilled will be considered a failure. If the function threw an error, it will be considered a failure.

toHaveReturnedWith(expected: unknown): void;Ensures that a mock function has returned a specific value. This matcher uses deep equality, like toEqual(), and supports asymmetric matchers.

toInclude(expected: string): void;Asserts that a value includes a string.

For non-string values, use toContain() instead.

@param expectedthe expected substring

toIncludeRepeated(expected: string,times: number): void;Asserts that a value includes a string {times} times.

@param expectedthe expected substring

@param timesthe number of times the substring should occur

toMatch(expected: string | RegExp): void;Asserts that a value matches a regular expression or includes a substring.

@param expectedthe expected substring or pattern.

expect("dog").toMatch(/dog/); expect("dog").toMatch("og"); toMatchInlineSnapshot(value?: string): void;Asserts that a value matches the most recent inline snapshot.

@param valueThe latest automatically-updated snapshot value.

expect("Hello").toMatchInlineSnapshot(); expect("Hello").toMatchInlineSnapshot(`"Hello"`); toMatchInlineSnapshot(propertyMatchers?: object,value?: string): void;Asserts that a value matches the most recent inline snapshot.

@param propertyMatchersObject containing properties to match against the value.

@param valueThe latest automatically-updated snapshot value.

expect({ c: new Date() }).toMatchInlineSnapshot({ c: expect.any(Date) }); expect({ c: new Date() }).toMatchInlineSnapshot({ c: expect.any(Date) }, ` { "v": Any, } `); toMatchObject(subset: object): void;Asserts that an object matches a subset of properties.

@param subsetSubset of properties to match with.

expect({ a: 1, b: 2 }).toMatchObject({ b: 2 }); expect({ c: new Date(), d: 2 }).toMatchObject({ d: 2 }); toMatchSnapshot(hint?: string): void;Asserts that a value matches the most recent snapshot.

@param hintHint used to identify the snapshot in the snapshot file.

expect([1, 2, 3]).toMatchSnapshot('hint message'); toMatchSnapshot(propertyMatchers?: object,hint?: string): void;Asserts that a value matches the most recent snapshot.

@param propertyMatchersObject containing properties to match against the value.

@param hintHint used to identify the snapshot in the snapshot file.

expect([1, 2, 3]).toMatchSnapshot(); expect({ a: 1, b: 2 }).toMatchSnapshot({ a: 1 }); expect({ c: new Date() }).toMatchSnapshot({ c: expect.any(Date) }); toSatisfy(predicate: (value: T) => boolean): void;Checks whether a value satisfies a custom condition.

@param predicateThe custom condition to be satisfied. It should be a function that takes a value as an argument (in this case the value from expect) and returns a boolean.

expect(1).toSatisfy((val) => val > 0); expect("foo").toSatisfy((val) => val === "foo"); expect("bar").not.toSatisfy((val) => val === "bun"); toStartWith(expected: string): void;Asserts that a value starts with a string.

@param expectedthe string to start with

toStrictEqual(expected: T): void;Asserts that a value is deeply and strictly equal to what is expected.

There are two key differences from toEqual():

It checks that the class is the same.It checks that undefined values match as well.@param expectedthe expected value

class Dog { type = "dog"; } const actual = new Dog(); expect(actual).toStrictEqual(new Dog()); expect(actual).toStrictEqual({ type: "dog" }); // fail toStrictEqualX = T>(expected: NoInferX>): void;toThrow(expected?: unknown): void;Asserts that a function throws an error.

If expected is a string or RegExp, it will check the message property.If expected is an Error object, it will check the name and message properties.If expected is an Error constructor, it will check the class of the Error.If expected is not provided, it will check if anything has thrown.@param expectedthe expected error, error message, or error pattern

function fail() { throw new Error("Oops!"); } expect(fail).toThrow("Oops!"); expect(fail).toThrow(/oops/i); expect(fail).toThrow(Error); expect(fail).toThrow(); toThrowError(expected?: unknown): void;Asserts that a function throws an error.

function fail() { throw new Error("Oops!"); } expect(fail).toThrowError("Oops!"); expect(fail).toThrowError(/oops/i); expect(fail).toThrowError(Error); expect(fail).toThrowError(); toThrowErrorMatchingInlineSnapshot(value?: string): void;Asserts that a function throws an error matching the most recent snapshot.

@param valueThe latest automatically-updated snapshot value.

function fail() { throw new Error("Oops!"); } expect(fail).toThrowErrorMatchingInlineSnapshot(); expect(fail).toThrowErrorMatchingInlineSnapshot(`"Oops!"`); toThrowErrorMatchingSnapshot(hint?: string): void;Asserts that a function throws an error matching the most recent snapshot.

function fail() { throw new Error("Oops!"); } expect(fail).toThrowErrorMatchingSnapshot(); expect(fail).toThrowErrorMatchingSnapshot("This one should say Oops!"); interface MatchersBuiltinT = unknown>fail: (message?: string) => voidAssertion which fails.