Testing a private method in typescript using jest throws an error

Asked Jun 09 '20 at 06:09

Active May 20 '21 at 03:11

Viewed 1,357 times

I want to test the check method which is a private method.

class Example {
  private check = async (x: string) => {
    //my code
  };
  public build() {
    const x: string = 'check';
    await this.check(x);
  }
}

Below is how i am testing the private method:

describe('Example', () => {
  it('should test the private method', () => {
    const handlePrivate = jest.spyOn(Example.prototype as any, 'check');

    expect(handlePrivate).toHaveBeenCalled();
  });
});

But an error is being thrown stating that

Cannot spy the check property because it is not a function; undefined given instead

edited May 20 '21 at 03:11

Lin Du

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asked Jun 09 '20 at 06:09

Sakshi

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does this answer your question? https://stackoverflow.com/questions/43265944/is-there-any-way-to-mock-private-functions-with-jest – Red Baron Jun 09 '20 at 06:16
@RedBaron i have already gone through this link,it wasn't of much help. – Sakshi Jun 09 '20 at 06:24
`Example.prototype` won't have the `check` because it is defined as instance member – Aleksey L. Jun 09 '20 at 06:29
Also you don't show how you create an instance within the test and actually call the method.. – Aleksey L. Jun 09 '20 at 06:32
@AlekseyL. i was following this https://stackoverflow.com/questions/56044471/testing-private-functions-in-typescript-with-jest – Sakshi Jun 09 '20 at 06:42
@AlekseyL. could you suggest something other than the method suggested in the above link ? – Sakshi Jun 09 '20 at 06:43
First you should the real test (when you create `new Example` and call the `build`) – Aleksey L. Jun 09 '20 at 09:03

Testing a private method in typescript using jest throws an error

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