How to test if a UIControlEvents has been fired

Question

I have a library implementing a custom UIControl with a method which would fire a .valueChanged event when called. I would like to test the method for that behavior.

My custom control:

class MyControl: UIControl {
    func fire() {
        sendActions(for: .valueChanged)
    }
}

And the test:

import XCTest

class ControlEventObserver: NSObject {
    var expectation: XCTestExpectation!

    init(expectation anExpectation: XCTestExpectation) {
        expectation = anExpectation
    }

    func observe() {
        expectation.fulfill()
    }
}

class Tests: XCTestCase {
    func test() {
        let myExpectation = expectation(description: "event fired")
        let observer = ControlEventObserver(expectation: myExpectation)
        let control = MyControl()
        control.addTarget(observer, action: #selector(ControlEventObserver.observe), for: .valueChanged)
        control.fire()
        waitForExpectations(timeout: 1) { error in
            XCTAssertNil(error)
        }
    }
}

The problem is the observe method never gets called so the expectation is not fulfilled.

The question is: how can we test for UIControlEvents like in this case? Perhaps we need to force the runloop somehow?

EDIT 1: Please note that since I am testing a library, my test target does not have any Host Application. The test above passes when the test target has a host application.

Answer 1

Apple's documentation for UIControl states that:

When a control-specific event occurs, the control calls any associated action methods right away. Action methods are dispatched through the current UIApplication object, which finds an appropriate object to handle the message, following the responder chain if needed.

When sendActions(for:) is called on a UIControl, the control will call the UIApplication's sendAction(_:to:from:for:) to deliver the event to the registered target.

Since I am testing a library without any Host Application, there is no UIApplication object. Hence, the .valueChanged event is not dispatched and the observe method does not get called.

Answer 2

You are declaring the observer object inside the test method. This means that as soon as the method completes it will be released from memory and hence is not called. Create a reference to the observer at class level in the Tests class as follows and it will work.

class Tests: XCTestCase {

    var observer: ControlEventObserver!
    func test() {
        let myExpectation = expectation(description: "event fired")
        self.observer = ControlEventObserver(expectation: myExpectation)
        let control = MyControl()
        control.addTarget(observer, action:#selector(ControlEventObserver.observe), for: .valueChanged)
        control.fire()
        waitForExpectations(timeout: 1) { error in
            XCTAssertNil(error)
        }
    }
}

You will also need the myExpectation & control to be declared in the same way else that won't be called either.