Cool thing about Swift initializers: you can call them using dot syntax and pass them as closures! Perfect for mocking dates in tests.

class Logger {
    private let storage: LogStorage
    private let dateProvider: () -> Date
    
    init(storage: LogStorage = .init(), dateProvider: @escaping () -> Date = Date.init) {
        self.storage = storage
        self.dateProvider = dateProvider
    }
    
    func log(event: Event) {
        storage.store(event: event, date: dateProvider())
    }
}