Logger component in LWC - need more info on implementation

[dbrennan-008]

I am fairly new to LWC and I am trying to use nebula logger in our LWC components.
Installed unlocked package in our sandbox dev env.
When I try to run jest test --> node ./node_modules/@salesforce/sfdx-lwc-jest/bin/sfdx-lwc-jest contactCreate.test.js
I am getting the following error
Cannot find module 'c/logger' from 'contact-app/main/default/lwc/contactCreate/contactCreate.html'

I have included the following at the top of my template markup

<template>
    <c-logger></c-logger>
   ...
   ...
   ...
</template>

And I am trying to use the following in .js

const logger = this.template.querySelector("c-logger");
logger.error("Error creating contact");

I am sure I am missing something really basic here, do I need to include something in my package.json? or something? can someone please help..

[jamessimone]

@dbrennan008 when you use packaged dependencies - like Nebula's <c-logger> component - you need to explicitly tell Jest how to mock it:

import Logger from 'c/logger';

jest.mock(
  'c/logger',
  () => ({
    error: jest.fn(),
    saveLog: jest.()
  }),
  { virtual: true }
);

Or something to that effect; you would then be able to say assert on the mocked version of Logger when testing the code-path where you're calling logger.error:

expect(Logger.error).toHaveBeenCalled();
// additional asserts about what's been passed to the error function, plus that saveLog was called

[jamessimone]

Note that I haven't compiled this code and it may be easier for you to follow one of the official stub examples (which explicitly extend LightningElement). If you do go this route, make sure to also see how you wire jest.config.js up to point to your explicit stubs.

[dbrennan-008]

Ah ok, that makes sense. Will try that out.
It will be quite helpful for folks like me if we can have tests for LWCDemo.
Thank you.

[dbrennan-008]

Here is a sample simple test and I am getting Assert Violation: c() 2nd argument Ctor must be a function. @jamessimone

import { createElement } from "lwc";
import My_Component from "c/My_Component";
import nLogger from "c/logger";

jest.mock(
'c/logger',
() => ({
error: jest.fn(),
saveLog: jest.fn()
}),
{ virtual: true }
);

describe('c-my-component', () => {

it('should log error and save log', () => {
// Instantiate the component
const element = createElement("c-my-component", {
is: My_Component
});
document.body.appendChild(element);

// Call the logError method
element.logError('Some error', 'Some details');

// Verify that c-logger.error was called with the correct arguments
expect(nLogger.error).toHaveBeenCalledWith('Some error', 'Some details');

// Verify that c-logger.saveLog was called
expect(nLogger.saveLog).toHaveBeenCalled();

});
});