bun:test Expect TypeScript interface | API Reference | Bun

You 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 {}
}

Access to negated asymmetric matchers.

expect("abc").toEqual(expect.stringContaining("abc")); // will pass
expect("abc").toEqual(expect.not.stringContaining("abc")); // will fail

Create 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

Create 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

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));
});

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());
});

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.

Ensures that a specific number of assertions are made

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).

Register new custom matchers.

An 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
});

Ensures that an assertion is made

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.

Matches any received string that contains the exact expected string

Matches any string that contains the exact provided string

Throw an error if this function is called.

Optional message to display if the test fails

never

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");
}
});

You can extend this interface with declaration merging, in order to add type support for custom 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 {}
}

Assertion which fails.

expect().fail();
expect().fail("message is optional");
expect().not.fail();
expect().not.fail("hi");

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();

Assertion which passes.

expect().pass();
expect().pass("message is optional");
expect().not.pass();
expect().not.pass("hi");

Expects the value to be a promise that rejects.

expect(Promise.reject("error")).rejects.toBe("error");

Expects the value to be a promise that resolves.

expect(Promise.resolve(1)).resolves.toBe(1);

Ensure that a mock function is called with specific arguments for the nth call.

Ensure that a mock function is called with specific arguments for the nth call.

Asserts that a value equals what is expected.

the 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

Asserts that a value is a array.

expect([1]).toBeArray();
expect(new Array(1)).toBeArray();
expect({}).not.toBeArray();

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);

Asserts that a value is a boolean.

expect(true).toBeBoolean();
expect(false).toBeBoolean();
expect(null).not.toBeBoolean();
expect(0).not.toBeBoolean();

Ensures that a mock function is called an exact number of times.

Ensure that a mock function is called with specific arguments.

Ensure that a mock function is called with specific arguments.

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.

the expected value

the 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.

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();

Asserts that a value is defined. (e.g. is not undefined)

expect(true).toBeDefined();
expect(undefined).toBeDefined(); // fail

Asserts that a value is empty.

expect("").toBeEmpty();
expect([]).toBeEmpty();
expect({}).toBeEmpty();
expect(new Set()).toBeEmpty();

Asserts that a value is an empty object.

expect({}).toBeEmptyObject();
expect({ a: 'hello' }).not.toBeEmptyObject();

Asserts that a number is even.

expect(2).toBeEven();
expect(1).not.toBeEven();

Asserts that a value is false.

expect(false).toBeFalse();
expect(true).not.toBeFalse();
expect(0).not.toBeFalse();

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();

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();

Asserts that a value is a function.

expect(() => {}).toBeFunction();

Asserts that a value is a number and is greater than the expected value.

the expected number

expect(1).toBeGreaterThan(0);
expect(3.14).toBeGreaterThan(3);
expect(9).toBeGreaterThan(9); // fail

Asserts that a value is a number and is greater than or equal to the expected value.

the expected number

expect(1).toBeGreaterThanOrEqual(0);
expect(3.14).toBeGreaterThanOrEqual(3);
expect(9).toBeGreaterThanOrEqual(9);

Asserts that the expected value is an instance of value

expect([]).toBeInstanceOf(Array);
expect(null).toBeInstanceOf(Array); // fail

Asserts that a value is a number, and is an integer.

expect(1).toBeInteger();
expect(3.14).not.toBeInteger();
expect(NaN).not.toBeInteger();

Asserts that a value is a number and is less than the expected value.

the expected number

expect(-1).toBeLessThan(0);
expect(3).toBeLessThan(3.14);
expect(9).toBeLessThan(9); // fail

Asserts that a value is a number and is less than or equal to the expected value.

the expected number

expect(-1).toBeLessThanOrEqual(0);
expect(3).toBeLessThanOrEqual(3.14);
expect(9).toBeLessThanOrEqual(9);

Asserts that a value is NaN.

Same as using Number.isNaN().

expect(NaN).toBeNaN();
expect(Infinity).toBeNaN(); // fail
expect("notanumber").toBeNaN(); // fail

Asserts that a value is a negative number.

expect(-3.14).toBeNegative();
expect(1).not.toBeNegative();
expect(NaN).not.toBeNegative();

Asserts that a value is null or undefined.

expect(null).toBeNil();
expect(undefined).toBeNil();

Asserts that a value is null.

expect(null).toBeNull();
expect(undefined).toBeNull(); // fail

Asserts that a value is a number.

expect(1).toBeNumber();
expect(3.14).toBeNumber();
expect(NaN).toBeNumber();
expect(BigInt(1)).not.toBeNumber();

Asserts that a value is an object.

expect({}).toBeObject();
expect("notAnObject").not.toBeObject();
expect(NaN).not.toBeObject();

Asserts that a number is odd.

expect(1).toBeOdd();
expect(2).not.toBeOdd();

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.

the expected value

expect(1).toBeOneOf([1,2,3]);
expect("foo").toBeOneOf(["foo", "bar"]);
expect(true).toBeOneOf(new Set([true]));

Asserts that a value is a positive number.

expect(1).toBePositive();
expect(-3.14).not.toBePositive();
expect(NaN).not.toBePositive();

Asserts that a value is a string.

expect("foo").toBeString();
expect(new String("bar")).toBeString();
expect(123).not.toBeString();

Asserts that a value is a symbol.

expect(Symbol("foo")).toBeSymbol();
expect("foo").not.toBeSymbol();

Asserts that a value is true.

expect(true).toBeTrue();
expect(false).not.toBeTrue();
expect(1).not.toBeTrue();

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();

Asserts that a value matches a specific type.

expect(1).toBeTypeOf("number");
expect("hello").toBeTypeOf("string");
expect([]).not.toBeTypeOf("boolean");

Asserts that a value is undefined.

expect(undefined).toBeUndefined();
expect(null).toBeUndefined(); // fail

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();

Asserts that a value is a number between a start and end value.

the start number (inclusive)

the end number (exclusive)

Asserts that a value contains what is expected.

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

the expected value

expect([1, 2, 3]).toContain(1);
expect(new Set([true])).toContain(true);
expect("hello").toContain("o");

Asserts that an object contains all the provided keys.

The value must be an object

the 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']);

Asserts that an object contain all the provided values.

The value must be an object

the 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']);

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

the 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']);

Asserts that an object contain any provided value.

The value must be an object

the 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']);

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.

the expected value

expect([{ a: 1 }]).toContainEqual({ a: 1 });
expect([{ a: 1 }]).not.toContainEqual({ a: 2 });

Asserts that an object contains a key.

The value must be an object

the 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');

Asserts that an object contains all the provided keys.

the 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']);

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.

the 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" }]);

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

the 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']);

Asserts that a value ends with a string.

the string to end with

Asserts that a value is deeply equal to what is expected.

the expected value

expect(100 + 23).toBe(123);
expect("d" + "og").toBe("dog");
expect([456]).toEqual([456]);
expect({ value: 1 }).toEqual({ value: 1 });

Asserts that a value is equal to the expected string, ignoring any whitespace.

the expected string

expect(" foo ").toEqualIgnoringWhitespace("foo");
expect("bar").toEqualIgnoringWhitespace(" bar ");

Ensures that a mock function is called.

Ensures that a mock function is called an exact number of times.

Ensure that a mock function is called with specific arguments.

Ensure that a mock function is called with specific arguments for the last call.

Ensure that a mock function is called with specific arguments for the nth call.

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.

Asserts that a value has a .length property that is equal to the expected length.

the expected length

expect([]).toHaveLength(0);
expect("hello").toHaveLength(4);

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.

The 1-based index of the function call

The expected return value

Asserts that a value has a property with the expected name, and value if provided.

the expected property name or path, or an index

the 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);

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.

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.

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

Asserts that a value includes a string.

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

the expected substring

Asserts that a value includes a string {times} times.

the expected substring

the number of times the substring should occur

Asserts that a value matches a regular expression or includes a substring.

the expected substring or pattern.

expect("dog").toMatch(/dog/);
expect("dog").toMatch("og");

Asserts that a value matches the most recent inline snapshot.

The latest automatically-updated snapshot value.

expect("Hello").toMatchInlineSnapshot();
expect("Hello").toMatchInlineSnapshot(`"Hello"`);

Asserts that a value matches the most recent inline snapshot.

Object containing properties to match against the value.

The 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,
}
`);

Asserts that an object matches a subset of properties.

Subset of properties to match with.

expect({ a: 1, b: 2 }).toMatchObject({ b: 2 });
expect({ c: new Date(), d: 2 }).toMatchObject({ d: 2 });

Asserts that a value matches the most recent snapshot.

Hint used to identify the snapshot in the snapshot file.

expect([1, 2, 3]).toMatchSnapshot('hint message');

Asserts that a value matches the most recent snapshot.

Object containing properties to match against the value.

Hint 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) });

Checks whether a value satisfies a custom condition.

The 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");

Asserts that a value starts with a string.

the string to start with

Asserts that a value is deeply and strictly equal to what is expected.

There are two key differences from toEqual():

the expected value

class Dog {
type = "dog";
}
const actual = new Dog();
expect(actual).toStrictEqual(new Dog());
expect(actual).toStrictEqual({ type: "dog" }); // fail

Asserts that a function throws an error.

the 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();

Asserts that a function throws an error.

the expected error, error message, or error pattern

function fail() {
throw new Error("Oops!");
}
expect(fail).toThrowError("Oops!");
expect(fail).toThrowError(/oops/i);
expect(fail).toThrowError(Error);
expect(fail).toThrowError();

Asserts that a function throws an error matching the most recent snapshot.

The latest automatically-updated snapshot value.

function fail() {
throw new Error("Oops!");
}
expect(fail).toThrowErrorMatchingInlineSnapshot();
expect(fail).toThrowErrorMatchingInlineSnapshot(`"Oops!"`);

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!");