Error in unit testing: Trying to access property 'pipe' of an undefined variable results in a TypeError

Recently, I've been faced with the challenge of writing a unit test for one of the functions in my component. The specific function in question is called 'setup', which internally calls another function named 'additionalSetup'. In 'additionalSetup', there's a subscription to the store with a pipe(take(1)) method snippet that captures the first emission:

private setup() {
    // ...declare/assign variables in the component
    this.additionalSetup();
}

private additionalSetup() {
    this.store.pipe(take(1)).subscribe(/*actual logic implementation*/);
}

However, running the unit test results in an error message:

TypeError: Cannot read property 'pipe' of undefined

To tackle this issue, I attempted to mock 'additionalSetup' within the 'setup' unit test like so:

component.additionalSetup = jest.fn();

Unfortunately, this approach did not yield the desired outcome. As someone relatively new to jest, I find myself still on a learning curve. What strategies or methods should I consider to address and resolve this particular error?

Answer №1

The component has already been created and component.additionalSetup has already been invoked. To resolve the issue, you will need to mock additionalSetup before creating the component.

You can achieve this easily using the Angular Testing Library

 const component = await render(MyComponent, {
    componentProperties: {
      additionalSetup : jest.fn(),
    },
  });

Alternatively, you can create your own implementation by following this guide here

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