class Object {
…
    func startListeningForNotifications() {
        NotificationCenter.default.addObserver(self, selector: #selector(Object.notificationReceived), name: NSNotification.Name(rawValue: "ObjectNotification"), object: nil)
    }
…
}

class ExampleTestCase: XCTestCase {
…
    func test_emulatateThrowingObjectNotification_then_getCurrentValue_returns_two() {
		object.startListeningForNotifications()
        emulateThrowingObjectNotification()
        XCTAssertEqual(object.getCurrentValue(), 2)
    }
…
}