XCTest: Testing async callbacks

gistfile1.txt

import XCTest
@testable import MyApp

class CallbackTest: XCTestCase {

  func testAsyncCalback() {
    let service = SomeService()

    // 1. Define an expectation
    let expectation = expectationWithDescription("SomeService does stuff and runs the callback closure")

    // 2. Exercise the asynchronous code
    service.doSomethingAsync { success in
      XCTAssertTrue(success)

      // Don't forget to fulfill the expectation in the async callback
      expectation.fulfill()
    }

    // 3. Wait for the expectation to be fulfilled
    waitForExpectationsWithTimeout(1) { error in
      if let error = error {
        XCTFail("waitForExpectationsWithTimeout errored: \(error)")
      }
    }
  }
}