     var location: String?
     var startDate: Date = Date()
     var endDate: Date = Date()
+
+    private(set) var addedRelativeAlarmTime: TimeInterval?
+    func addAlarm(relativeOffsetFromStartDate relativeOffset: TimeInterval) {
+        addedRelativeAlarmTime = relativeOffset
+    }
     
 }
 

        calendarEvent.startDate = event.StartDateTimeUtc
        calendarEvent.endDate = event.EndDateTimeUtc

        calendar.save(event: calendarEvent)
    }



        XCTAssertTrue(eventAssertion.isSatisfied)
    }

    func testTheEventIsGivenAnAlarmWithHalfAnHourPriorToTheStartTime() {
        let event = makeEventWithValues()
        let expectedRelativeOffsetFromStartTime: TimeInterval = -1800
        let assertion: (CalendarEvent) -> Bool = { event in
            return (event as? StubCalendarEvent)?.addedRelativeAlarmTime == expectedRelativeOffsetFromStartTime
        }

        let eventAssertion = makeCalendarEventCreationTest(event: event,
                                                           assertion: assertion)

        XCTAssertTrue(eventAssertion.isSatisfied)
    }
    
}
