`toBeInstanceOf(Number)` does not work in jest

Question

I have a test as follows:

expect(result.data.quota).toBeInstanceOf(Number);

This test fails with a weird error saying the a Number was expected and a Number was received:

 expect(value).toBeInstanceOf(constructor)

    Expected constructor: Number
    Received constructor: Number
    Received value: 2000

Reynicke · Accepted Answer · 2019-09-16T13:40:58.150

46

expect(value).not.toBeNaN();

Edit: I would go with @bszoms solution:

expect(typeof value).toBe('number')

edited Sep 16 '19 at 13:40

answered Sep 28 '18 at 08:48

Reynicke

8

This is wrong. False is not NaN but also not a number, for example. – Marcos Pereira Apr 23 '19 at 17:00
3

This answer must clearly be avoided. This will make your tests successful for *ANYTHING* but NaN. `false`, `"some string"`, `true`, `Promise`, `ReactComponent` you name it – Lukas Sep 04 '19 at 16:09

stephan · Answer 2 · 2019-05-27T14:46:57.673

44

The following works for all constructors:

expect(value).toEqual(expect.any(Number));

edited May 27 '19 at 14:46

answered May 14 '19 at 14:57

stephan

score 24 · Answer 3 · answered Nov 19 '18 at 12:46

24

You can also do this: expect(typeof <value>).toBe('number')

Or you can use jest-extended, which adds a whole range of matchers including toBeNumber.

Both courtesy of the discussion here.

answered Nov 19 '18 at 12:46

maltem-za

score 2 · Answer 4 · answered Sep 04 '19 at 16:06

2

Taking @stephan's anwer, this works for async / promise based methods:

await expect(asyncFunction()).resolves.toEqual(expect.any(Number));

answered Sep 04 '19 at 16:06

Lukas

4 Answers4