How do I test super calls when using Typescript with Jest?

user_8126238 0
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Say I have a class that's structured like this: 

// Some class that calls super.get() and adds an additional param
export default class ClassB extends ClassA {
   private foo: string;

   constructor(params) {
      super(params);
      this.foo = 'bar';
   }

   public async get(params?: { [key: string]: any }): Promise<any> {
      return super.get({
         foo: this.foo,
         ...params,
      });
   }
}

I would like to test that super.get() was called with the provided parameters as well as the additional { foo: 'bar' }.

import ClassA from '../../src/ClassA';
import ClassB from '../../src/ClassB';

jest.mock('../../src/ClassA');
jest.unmock('../../src/ClassB');

describe('ClassB', () => {
   describe('get', () => {
      beforeAll(() => {
        // I've tried mock implementation on classA here but didn't have much luck
        // due to the extending not working as expected 
      });
      it('should get with ClassA', async () => {
         const classB = new ClassB();
         const response = await classB.get({
           bam: 'boozled',
         });
         // Check if classA fetch mock called with params?
      });
   });
});

How do I check that classA.fetch was actually called with the params I'm expecting?

Am I doing anything that's just completely wrong?

Thanks for any help!

ts-jest jestjs typescript mocking
1 Answers

You can accomplish this by spying on the prototype of the extended class, something like this: 

const classASpy = jest.spyOn(ClassA.prototype, 'get');
classB.get(param)
expect(classASpy).toHaveBeenCalledWith(param);

Hope it helps!

user_92784930
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