Task Scheduler with Swift 2.3

TaskScheduler.swift

public class TaskScheduler: NSObject {

    weak var timer: NSTimer? = nil
    var task: ((NSTimer) -> Void)?
    
    public func schedule(interval: NSTimeInterval, repeats: Bool, task: ((NSTimer) -> Void)? = nil) -> NSTimer? {
        if !NSThread.isMainThread() {
            return nil
        }

        self.task = task
        timer = NSTimer.scheduledTimerWithTimeInterval(interval, target: self, selector: #selector(tick(_:)), userInfo: nil, repeats: repeats)
        return timer
    }
    
    public func tick(timer: NSTimer) {
        task?(timer)
    }
    
}

TaskSchedulerTests.swift

import XCTest

import MyApp

class TaskSchedulerTests: XCTestCase {
    
    override func setUp() {
        super.setUp()
        // Put setup code here. This method is called before the invocation of each test method in the class.
    }
    
    override func tearDown() {
        // Put teardown code here. This method is called after the invocation of each test method in the class.
        super.tearDown()
    }
  
    func testTaskScheduler() {
        let expectation = self.expectationWithDescription("Timer")
        
        var count: Int = 0
        let taskScheduler = TaskScheduler()
        let timer = taskScheduler.schedule(0.25, repeats: true) { timer in
            count += 1
            if count == 5 {
                timer.invalidate()
                expectation.fulfill()
            }
        }
        
        XCTAssertNotNil(timer)
        
        let timeout: NSTimeInterval = 5
        self.waitForExpectationsWithTimeout(timeout) { (error) in
            if let error = error {
                print("Error: \(error)")
            }
        }
    }
    
}