perform_button_action.swift

// On the view's code
lazy var actionButton: UIButton = {
    let button = UIButton()
    button.addTarget(self, action: #selector(didTapActionButton), for: .touchUpInside)
    return button
}()

// On the test code
func test_pressingActionButton_shouldCallDelegate() {
    let button = view.actionButton
    let action = button.actions(forTarget: sut, forControlEvent: .touchUpInside)?.first ?? ""
    
    sut.performSelector(onMainThread: Selector(action), with: nil, waitUntilDone: true)
    
    XCTAssertTrue(delegateSpy.actionCalled)
}