Error is thrown but Jest's `toThrow()` does not capture the error

Question

Here is my error codes:

 FAIL  build/__test__/FuncOps.CheckFunctionExistenceByString.test.js
  ● 
    expect(CheckFunctionExistenceByStr(
      'any string', 'FunctionThatDoesNotExistsInString'
    )).toThrow();


    Function FunctionThatDoesNotExistsInString does not exists in string.

      at CheckFunctionExistenceByStr (build/FuncOps.js:35:15)
      at Object.<anonymous> (build/__test__/FuncOps.CheckFunctionExistenceByString.test.js:12:51)
          at new Promise (<anonymous>)
          at <anonymous>

As you can see the error did indeed occurred: Function FunctionThatDoesNotExistsInString does not exists in string.. However it is not captured as a pass in Jest.

Here is my codes:

test(`
    expect(CheckFunctionExistenceByStr(
      'any string', 'FunctionThatDoesNotExistsInString'
    )).toThrow();
  `, () => {
    expect(CheckFunctionExistenceByStr(
      'any string', 'FunctionThatDoesNotExistsInString'
    )).toThrow();
  }
);

score 48 · Accepted Answer · answered Nov 20 '17 at 17:58

expect(fn).toThrow() expects a function fn that, when called, throws an exception.

However you are calling CheckFunctionExistenceByStr immediatelly, which causes the function to throw before running the assert.

Replace

test(`
    expect(CheckFunctionExistenceByStr(
      'any string', 'FunctionThatDoesNotExistsInString'
    )).toThrow();
  `, () => {
    expect(CheckFunctionExistenceByStr(
      'any string', 'FunctionThatDoesNotExistsInString'
    )).toThrow();
  }
);

with

test(`
    expect(() => {
      CheckFunctionExistenceByStr(
        'any string', 'FunctionThatDoesNotExistsInString'
      )
    }).toThrow();
  `, () => {
    expect(() => {
      CheckFunctionExistenceByStr(
        'any string', 'FunctionThatDoesNotExistsInString'
      )
    }).toThrow();
  }
);

This helps: https://facebook.github.io/jest/docs/en/expect.html#tothrowerror -- Encapsulate the method you are actually want to test inside another function. Place that outer function inside expect() without calling it (no trailing parenthesis). — fuma, Mar 23 '18 at 15:08

leonheess · Answer 2 · 2023-02-14T01:01:25.837

40

Jest needs a callback function here. Instead of passing the function definition like this:

expect(yourFunction(args)).toThrow(ErrorTypeOrErrorMessage)

Do this:

expect(() => yourFunction(args)).toThrow(ErrorTypeOrErrorMessage)

If you don't need to pass arguments you can also do:

expect(yourFunction).toThrow(ErrorTypeOrErrorMessage)

And for asynchronous functions:

expect(async () => await yourFunction(args)).rejects.toThrow(ErrorTypeOrErrorMessage)

edited Feb 14 '23 at 01:01

answered Feb 08 '21 at 21:47

leonheess

16,068
14
77
112

1

Thank you! This helped me from pulling all my hair out! – Brigante May 27 '21 at 08:59
2

I think they should add this to their documentation. – Namrata Sep 27 '21 at 08:04
I also had to change my code from `.rejects` to `.toThrow` but the arrow function is required as well. – fIwJlxSzApHEZIl Feb 22 '22 at 19:38

score 8 · Answer 3 · answered Apr 07 '22 at 07:44

had a similar issue but my function to be tested is async and hence your expect have to look like this:

await expect(async () => {await myFunctionToBeTested();}).rejects.toThrow('My Error message')

the solution I got from here

Note:

the await before expect I added 'cause Eslint was complaining but would work without it.

score 0 · Answer 4 · answered May 11 '22 at 14:25

0

For me, the problem was that the function I was testing was a getter that was immediately executed even when omitting the (). Wrapping the getter in a closure (() => {myClass.get}) fixed the problem.

answered May 11 '22 at 14:25

Niek

1,464
1
17
27

Error is thrown but Jest's `toThrow()` does not capture the error

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