Components using Date objects produce different snapshots in different timezones

I’m using Enzyme with enzyme-to-json to do Jest snapshot testing of my React components. I’m testing shallow snapshots of a DateRange component that renders a display field with the current range (e.g. 5/20/2016 - 7/18/2016) and two DateInput components that allow selecting a Date value. This means that my snapshot contains the Dates I pass to the component both in the DateInput props and in a text representation it resolves itself. In my test I’m creating some fixed dates using new Date(1995, 4, 23).

When I run my test in different timezones, this produces different snapshots, because the Date(year, month, ...) constructor creates the date in the local timezone. E.g. use of new Date() produces this difference in snapshot between runs in my local timezone and on our CI server.

- value={1995-05-22T22:00:00.000Z}
+ value={1995-05-23T00:00:00.000Z}

I tried removing the timezone offset from the dates, but then the snapshot differed in the display field value, where the local timezone-dependent representation is used.

- value={5/20/2016 - 7/18/2016}
+ value={5/19/2016 - 7/17/2016}

How can I make my tests produce the same Dates in snapshots regardless of the timezone they’re run in?

Answer

I struggled with this for hours/days and only this worked for me:

1) In your test:

Date.now = jest.fn(() => new Date(Date.UTC(2017, 7, 9, 8)).valueOf())

2) Then change the TZ env var before running your tests. So the script in my package.json:

• (Mac & Linux only)

  "test": "TZ=America/New_York react-scripts test --env=jsdom",
  

• (Windows)

  "test": "set TZ=America/New_York && react-scripts test --env=jsdom",