jest test case is failing for react functional component

Question

My code is failing when i run this test. I have tried

await expect(API().isFileAvailable).rejects.toEqual(Promise.reject(new Error('Bad input')));

But this doesn't work

File: async (a: string, b: string | undefined, c: string | undefined) => {
        if (!a&& !b) {
            return Promise.reject(new Error('Bad input'));
        }
}

Did you read Jest's documentation? https://jestjs.io/docs/expect#rejects — Drarig29, Aug 28 '22 at 14:25
Also, when using a Promise with `async`, we generally don't use `Promise.reject()` but prefer to `throw`. — Drarig29, Aug 28 '22 at 14:26

score 0 · Answer 1 · answered Aug 28 '22 at 14:35

According to Jest's documentation, the rejects keyword should be used with toThrow() (which is an alias to toThrowError()).

You can directly use a string to match the error message, or a regex, or a Error object.

Your assertion should work with the following:

await expect(API().isFileAvailable).rejects.toThrow('Bad input');

Also, you should probably use throw in your code. Using Promise.reject() is less readable and the benefits of async/await is precisely to automatically reject when you throw an error.

File: async (a: string, b: string | undefined, c: string | undefined) => {
        if (!a&& !b) {
            // return Promise.reject(new Error('Bad input'));
            throw new Error('Bad input');
        }
}

jest test case is failing for react functional component

1 Answers1