Mrthdrb

I've been looking to start unit testing the Lightning Web Component I've created with LWC Jest and I am running into some issues in creating my component that is making use of the NavigationMixin module. The unit test is failing to create the component when it reaches the NavigationMixin.GenerateUrl with the following error:

TypeError: Cannot read property 'then' of undefined

 64 | "title" : this.linkTitles.shift(),
 65 | "location" : pageRef,
 > 66 | "url" : this[NavigationMixin.GenerateUrl](pageRef).then(url => this.links[i].url = url;),
 | ^
 67 | "description" : this.linkDescriptions.shift()

I've tried wrapping the 'expect' assertion in a Promise statement as suggested here due to the asynchronous nature of NavigationMixin.GenerateUrl but had no luck. Tried to implement some of the jest.js mocking examples as well but didn't have much luck.

The following is the unit test and Javascript involved.
Full component source is here.

Unit Test:

// createElement is what we'll use to create our component under test
import createElement from 'lwc';
// helpfulLinks is the component being tested
import helpfulLinks from 'c/helpfulLinks';

describe('Helpful Links Component', () => 
 it('is chained to another component', () => 
 // Given
 const expectedClassName = 'slds-grid slds-wrap slds-color__background_gray-1 slds-box pull-up-margin';
 // When
 const element = createElement('c-helpful-links', is: helpfulLinks );
 element.linkIcons = 'doctype:pdf;doctype:flash';
 element.linkTitles = 'Sample Title; Sample Title';
 element.linkUrlsOrIds = '/;/';
 element.linkDescriptions = 'Sample Description;Sample Description';
 element.chainLists = true;
 document.body.appendChild(element);
 const className = element.shadowRoot.querySelector('div[data-id=linksList]').className;
 // Then
 expect(className).resolves.toBe(expectedClassName);
 );
);

Javascript for the Component

import LightningElement, api, track from 'lwc';
import NavigationMixin from 'lightning/navigation';

export default class HelpfulLinks extends NavigationMixin(LightningElement) 
 //All of the settings that can be defined for the component
 @api title;
 @api navigationOptions;
 @api showTitle;
 @api chainLists;
 @api
 get linkIcons() 
 return this._linkIcons;
 
 set linkIcons(value) 
 this._linkIcons = value.split(";");
 //Use this value to compare the lengths across all other settings
 this._linkSettingsCount = this._linkIcons.length;
 
 @api
 get linkTitles() 
 return this._linkTitles;
 
 set linkTitles(value) 
 this._linkTitles = value.split(";");
 
 @api
 get linkUrlsOrIds() 
 return this._linkUrlsOrIds;
 
 set linkUrlsOrIds(value) 
 this._linkUrlsOrIds = value.split(";");
 
 @api
 get linkDescriptions() 
 return this._linkDescriptions;
 
 set linkDescriptions(value) 
 this._linkDescriptions = value.split(";");
 

 //Holds the constructed links to be rendered. Needs to be tracked for the URL display to work.
 @track
 links = [];

 //Used to return an error back to the user
 errorOccurred = false;
 errorMessage = '';

 renderedCallback() 
 //With the DOM being rendered, check whether the lists should be chained
 if(this.chainLists) 
 this.template.querySelector('div[data-id=linksList]').className = this.template.querySelector('div[data-id=linksList]').className + ' pull-up-margin';
 
 

 connectedCallback() 
 //Check that all the link settings are the same length
 if([this.linkIcons, this.linkTitles, this.linkUrlsOrIds, this.linkDescriptions].every(this.linkLengthSettingsMatch, this)) 
 //Set the links
 for(let i = 0; i < this._linkSettingsCount; i++) 
 let pageRef = this.constructPageRef(this.linkUrlsOrIds.shift());
 this.links.push(
 "icon" : this.linkIcons.shift(),
 "title" : this.linkTitles.shift(),
 "location" : pageRef,
 "url" : this[NavigationMixin.GenerateUrl](pageRef).then(url => this.links[i].url = url;),
 "description" : this.linkDescriptions.shift()
 );
 
 
 else 
 //Set the error
 this.errorOccurred = true;
 this.errorMessage = 'Please ensure that when you fill out the icons, titles, urls and descriptions that they all have the same amount of semi colons.';
 
 

 navigateToTarget(event) 
 //Stop the event's default behavior.
 event.preventDefault();
 //Stop the event from bubbling up in the DOM.
 event.stopPropagation();
 //Navigate to the record page.
 this[NavigationMixin.Navigate](this.links[event.target.dataset.recordcount].location);
 

 constructPageRef(urlOrId) 
 switch(this.navigationOptions) 
 case "URL":
 return 
 type: 'standard__webPage',
 attributes: 
 url: urlOrId
 
 ;
 case "Salesforce File":
 return 
 type: 'standard__namedPage',
 attributes: 
 pageName: 'filePreview'
 ,
 state : 
 recordIds: urlOrId
 
 ;
 case "Record Page":
 return 
 type: 'standard__recordPage',
 attributes: 
 recordId: urlOrId,
 actionName: 'view'
 
 ;
 default:
 //As these switch values are guaranteed, this should never happen
 return null;
 
 

 //Utility for checking setting lengths
 linkLengthSettingsMatch(setting) 
 return setting.length === this._linkSettingsCount;
 

Any assistance on this would be greatly appreciated. Thanks!

The default mock implementation for NavigationMixin doesn't provide a promise.

You'll have to create your own mock implementation, either globally for your project, or specific to your component, which then works for your use case. As it's not about testing NavigationMixin you should run the latter approach.