testing component with react-day-picker produce warnings

Question

What API for dates does react-day-picker use? I'm mocking Date in my test as

    global.Date = class extends Date {
      constructor(date: string) {
        super(date);
        return date ? this : fromUnixTime(946684800);
      }
    } as DateConstructor;
    global.Date.now = jest.fn(() => 946684800000);

here and keep getting console warning: Encountered two children with the same key, 197001. I see that dates in calendar are actually correct, but aria-label="Thu Jan 01 1970" Seems that my date mock breaks the library.

Any ideas?

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