Jest - restore original moment function in one test - jestjs

Question

How can I restore or implement mock in one test? I have a function:
const parser = (data)=>{
const now = moment().format('DD-MM-YYYY');
//more implementation
const parsedDate = moment(dateFromData).format('DD-MM-YYYY')
return {
date: isDateFromDataExists ? now : parsedDate
}
}
And now I would like to test my function. When isDateFromDataExists is true I would like to return current year (which should be mocked), but when isDateFromDataExists is false I would like to return parsedDate.
When I mocked globally
jest.mock('moment', () => () => ({format: () => '01-01-2020'}));
I can't "unlock" in one test.
How can I do this with Jest?
====EDIT====
This is my code.
const myParser = (single) => {
const obj = {};
const now = moment().format("DD-MM-YYYY");
obj.availableFrom = get(single, 'FreeFrom', '') !== '' ? moment(get(single, 'FreeFrom'), 'YYYY-MM-DD').format("DD-MM-YYYY") : now;
return obj;
}
This is my tests
test('Return correct json when FreeFrom is empty', async () => {
const xmlData = fs.readFileSync(path.join(__dirname, './testData/1.xml'), 'utf8');
var jsonObj = parser.parse(xmlData, options, true);
const result = require('./testData/1.json');
expect(myParser(jsonObj)).toEqual(result);
});
test('Return correct json when FreeFrom is available', async () => {
const xmlData = fs.readFileSync(path.join(__dirname, './testData/2.xml'), 'utf8');
var jsonObj = parser.parse(xmlData, options, true);
const result = require('./testData/2.json');
expect(myParser(jsonObj)).toEqual(result);
});
I have to cover two test cases.
When FreeFrom is not empty string then convert value with moment. Then format to my format.
When FreeFrom is empty string then use current date with moment. Then format to my format.
In case 2. I would like to mock current date to make tests independent of system date.

Answer 1

As suggested in the comments check related question
Here's how you could implement it
let dateFromData = null;
let isDateFromDataExists = null;
const parser = (data) => {
const now = moment().format('DD-MM-YYYY');
const parsedDate = moment(dateFromData, 'DD-MM-YYYY').format('DD-MM-YYYY')
return {
date: isDateFromDataExists ? now : parsedDate
}
}
const {
core: {
beforeEach,
describe,
it,
expect,
run
},
} = window.jestLite;
describe("parser", () => {
beforeEach(() => {
const currentTimestamp = moment().valueOf();
moment.now = jestLite.core.jest.fn().mockReturnValue(currentTimestamp);
});
it("return current date when isDateFromDataExists is true", () => {
isDateFromDataExists = true;
const currentDate = moment().format('DD-MM-YYYY');
expect(parser().date).toBe(currentDate);
});
it("return parsed date when isDateFromDataExists is false", () => {
isDateFromDataExists = false;
dateFromData = "02-01-2003";
expect(parser().date).toBe(dateFromData);
});
});
run().then(result => {
console.log(result);
})
<script src="https://unpkg.com/jest-lite#1.0.0-alpha.4/dist/core.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.19.1/moment.min.js"></script>