ReaderViewControllerTestCase.swift

override func setUp() {
    super.setUp()
    let mainStoryboard = UIStoryboard(name: "Main", bundle: nil)
    readerVC = mainStoryboard.instantiateViewController(withIdentifier: "ReaderViewController") as! ReaderViewController

    readerVC.dataSource = MockDataSource()
    readerVC.codeReader = mockReader
    
    //force the life cycle to be called
    let window = UIApplication.shared.delegate!.window!
    window!.rootViewController = readerVC
}

func testItFiresRightEventWhenKnownCodeIsRead() {
    let exp = expectation(description: "calls didFindCard")

    //given
    var didFindCardWasCalled = false
    readerVC.didFindCard = { _ in
        didFindCardWasCalled = true
        exp.fulfill()
    }
    //when
    mockReader.completion?("123")

    //then
    waitForExpectations(timeout: 3) { error in
        XCTAssert(didFindCardWasCalled)
        XCTAssertNil(error)
    }

}