How to mock the HTML5 File object with Jest

I have a lot of code passing around HTML 5 file objects. I wrote a suite of tests for it, however, it breaks my snapshot testing because of the File objects last modified date.

I attempted to mock using:

jest.mock('File', () => {
    return class MockFile {
        filename: string;

        constructor(parts: (string | Blob | ArrayBuffer | ArrayBufferView)[], filename: string, properties?: FilePropertyBag) {
            this.filename = filename;
        }
    }
});

I get errors saying the File module isn't found (I don't need to import it anywhere I use it...)

I also tried extending the file class and overriding the lastmodified get property, and it didn't seem to fix my snapshots.

What's the best way to handle this?

You just need to set File in the global namespace:

global.File = class MockFile {
    filename: string;
    constructor(parts: (string | Blob | ArrayBuffer | ArrayBufferView)[], filename: string, properties ? : FilePropertyBag) {
      this.filename = filename;
    }
  }