The easiest way to mock moment() and any function that it uses (i.e. .day(), .format()) is to change the Date that moment() uses under the hood
Add the snippet below inside your test file
Date.now = jest.fn(() => new Date("2020-05-13T12:33:37.000Z"));
This makes it so anytime moment() is called in your tests, moment() thinks that today is Wednesday, May 13th 2020