Evaluating whether an imported function, which serves as a dependency of an adapter, is being invoked with accurate parameters within the adapter using the Jest testing framework

Here is how my test looks

import { SlugGeneratorAdapter } from './slug-generator-adapter'
import slugify from 'slugify'

describe('SlugGenerator Adapter', () => {
  test('Should call the slug generator with the correct parameters.', () => {
    const target = new SlugGeneratorAdapter()

    const slugifySpy = jest.fn(slugify)

    target.generate('any text')
    expect(slugifySpy).toHaveBeenCalledWith('any text')
  }

  )
})

Another relevant class I have is as follows:

import slugify from 'slugify'
import { SlugGenerator } from '../../data/protocols/slug-generator'

export class SlugGeneratorAdapter implements SlugGenerator {
  generate (param: string): string {
    slugify(param)
    return 'any_value'
  }
}

I am struggling with implementing this test due to my limited knowledge of Jest. The failing issue seems to be related to slugify never being called (as far as I can tell). For those unfamiliar, slugify is a function that adds dashes to a string.

As an example, you can see how it works below:

 import slugify from 'slugify'

 slugify('any text more text') it returns // any-text-more-text

Answer №1

To effectively monitor the behavior of a function using `jest.spyOn`, you must provide an object and its corresponding method name. For instance, if you wish to spy on the `default` member, you can implement this:

import * as example from 'example'
const exampleSpy = jest.spyOn(example, 'default')

// ... perform action ...
expect(exampleSpy).toHaveBeenCalledWith('....')

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