how to deal with testing that uses uuid inside the component - vue.js

Question

I try to test my component that has a function to add an item to the array and each of those items has UUID property but I get this error when I try to run the unit test for that.
TypeError: Cannot read property 'v1' of undefined
const basicDataItem = {
> 380 | id: this.$uuid.v1()
How can I test the code that uses UUID like in this case?
edit:
this is the function that I want to test
addDataItem(key) {
const basicDataItem = {
id: this.$uuid.v1(),
units: '',
price: '',
label: '',
};
this.editableData[key].push(basicDataItem);
}

Answer 1

Here is a unit test solution for your case:
index.js:
export class SomeClass {
editableData = {
jest: []
};
$uuid = {
v1() {
return 'real uuid';
}
};
addDataItem(key) {
const basicDataItem = {
id: this.$uuid.v1(),
units: '',
price: '',
label: ''
};
this.editableData[key].push(basicDataItem);
}
}
index.spec.js:
import { SomeClass } from './';
describe('SomeClass', () => {
test('should add data item', () => {
const someClassInstance = new SomeClass();
const uuidv1Spy = jest.spyOn(someClassInstance.$uuid, 'v1').mockReturnValueOnce('fake uuid');
someClassInstance.addDataItem('jest');
expect(uuidv1Spy).toBeCalledTimes(1);
expect(someClassInstance.editableData).toEqual({ jest: [{ id: 'fake uuid', units: '', price: '', label: '' }] });
});
});
Unit test result with coverage report:
PASS src/stackoverflow/58710736/index.spec.js
SomeClass
✓ should add data item (14ms)
----------|----------|----------|----------|----------|-------------------|
File | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s |
----------|----------|----------|----------|----------|-------------------|
All files | 88.89 | 100 | 66.67 | 87.5 | |
index.js | 88.89 | 100 | 66.67 | 87.5 | 7 |
----------|----------|----------|----------|----------|-------------------|
Test Suites: 1 passed, 1 total
Tests: 1 passed, 1 total
Snapshots: 0 total
Time: 3.909s, estimated 6s
Source code: https://github.com/mrdulin/jest-codelab/tree/master/src/stackoverflow/58710736