Slightly different results for dateAt(.endOfDay) and dateAtEndOf(.day)

[Robuske]

While I was testing something I was not sure if Date().dateAt(.endOfDay) and Date().dateAtEndOf(.day) produced the same result, so I tried comparing them like this

XCTAssertEqual(Date().dateAt(.endOfDay), Date().dateAtEndOf(.day))

Which produced the error

XCTAssertEqual failed: ("2020-01-04 02:59:59 +0000") is not equal to ("2020-01-04 02:59:59 +0000")

Which seemed odd, using

XCTAssertEqual(Date().dateAt(.endOfDay).timeIntervalSince1970, Date().dateAtEndOf(.day).timeIntervalSince1970)

It shows the problem

XCTAssertEqual failed: ("1578106799.0") is not equal to ("1578106799.999")

From what I looked trough, they don't use the same implementation, which does not seem like a good idea and can lead to unexpected problems.

(I realise that date comparison should be done using methods proper for that, but these two should not differ)