Calendar extension to determine wether a date is after today

Calendar.swift

import Foundation

extension Calendar {
  /// Returns `true` if the given date is after today, as defined by the calendar and calendar's locale.
  ///
  /// Because it's impossible to define the end of a day (there are an infinite number of
  /// milliseconds between 23:59:59 and 00:00:00), this method instead ensures that 
  /// `date` >= `startOfTomorrow`.
  ///
  /// - parameter date: The specified date.
  /// - returns: `true` if the given date is after today
  func isDateAfterToday(_ date: Date) -> Bool {
    let startOfToday = startOfDay(for: Date())
    guard let startOfTomorrow = self.date(
      byAdding: .day,
      value: 1,
      to: startOfToday
    ) else {
      return false
    }

    switch compare(date, to: startOfTomorrow, toGranularity: .day) {
    case .orderedSame, .orderedAscending:
      return false
    case .orderedDescending:
      return true
    }
  }
}

CalendarTest.swift

import Foundation
import XCTest

class CalendarTest: XCTestCase {
  func testIsAfterToday() {
    let calendar = Calendar(identifier: .gregorian)

    XCTAssertTrue(calendar.isDateAfterToday(.distantFuture))
  }

  func testIsBeforeToday() {
    let calendar = Calendar(identifier: .gregorian)

    XCTAssertFalse(calendar.isDateAfterToday(.distantPast))
  }

  func testIsToday() {
    let calendar = Calendar(identifier: .gregorian)

    XCTAssertFalse(calendar.isDateAfterToday(Date()))
  }

  func testWithStartOfTomorrow() {
    let calendar = Calendar(identifier: .gregorian)
    let startOfToday = calendar.startOfDay(for: Date())
    let startOfTomorrow = calendar.date(byAdding: .day, value: 1, to: startOfToday)!

    XCTAssertTrue(calendar.isDateAfterToday(startOfTomorrow))
  }

  func testWithApproximateEndOfToday() {
    let calendar = Calendar(identifier: .gregorian)
    let approximateEndOfToday = calendar.date(
      bySettingHour: 23,
      minute: 59,
      second: 59,
      of: Date()
    )!

    XCTAssertFalse(calendar.isDateAfterToday(approximateEndOfToday))
  }
}