LayoutTests.swift

import XCTest

var myExpectation: XCTestExpectation? = nil

class Label: UILabel {

    override func invalidateIntrinsicContentSize() {
        super.invalidateIntrinsicContentSize()
        myExpectation = XCTestExpectation(description: "\(String(describing: text))")
    }

    override func layoutSubviews() {
        super.layoutSubviews()
        myExpectation!.fulfill()
    }
}

class MyView1: UIView {

    let iconView: UIView = UIView()
    let label = Label()

    let stackView = UIStackView()

    override init(frame: CGRect = .zero) {
        super.init(frame: frame)

        stackView.axis = .horizontal
        stackView.addArrangedSubview(iconView)
        stackView.addArrangedSubview(label)

        iconView.backgroundColor = .green
        iconView.heightAnchor.constraint(equalToConstant: 30).isActive = true
        iconView.widthAnchor.constraint(equalToConstant: 30).isActive = true

        label.backgroundColor = .blue

        addSubview(stackView)
        stackView.translatesAutoresizingMaskIntoConstraints = false
        stackView.topAnchor.constraint(equalTo: topAnchor).isActive = true
        stackView.leftAnchor.constraint(equalTo: leftAnchor).isActive = true

    }

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
}

class MyView2: UIView {
    let iconView: UIView = UIView()
    let label = Label()

    override init(frame: CGRect = .zero) {
        super.init(frame: frame)

        addSubview(iconView)
        addSubview(label)

        iconView.backgroundColor = .green
        iconView.translatesAutoresizingMaskIntoConstraints = false
        iconView.heightAnchor.constraint(equalToConstant: 30).isActive = true
        iconView.widthAnchor.constraint(equalToConstant: 30).isActive = true
        iconView.topAnchor.constraint(equalTo: topAnchor).isActive = true
        iconView.leftAnchor.constraint(equalTo: leftAnchor).isActive = true

        label.translatesAutoresizingMaskIntoConstraints = false
        label.topAnchor.constraint(equalTo: topAnchor).isActive = true
        label.leftAnchor.constraint(equalTo: iconView.rightAnchor).isActive = true
        label.heightAnchor.constraint(equalToConstant: 30).isActive = true
        label.backgroundColor = .blue
    }

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
}

class MyView3: UIView {
    let iconView: UIView = UIView()
    let label = Label()

    override init(frame: CGRect = .zero) {
        super.init(frame: frame)

        addSubview(iconView)
        addSubview(label)

        iconView.backgroundColor = .green
        label.backgroundColor = .blue

        iconView.frame = CGRect(x: 0, y: 0, width: 30, height: 30).integral
    }

    override func layoutSubviews() {
        super.layoutSubviews()

        let labelSize = label.sizeThatFits(CGSize(width: CGFloat.infinity, height: CGFloat.infinity))
        label.frame = CGRect(x: iconView.frame.maxX, y: 0, width: labelSize.width, height: 30).integral
    }

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
}

class StackViewTest2Tests: XCTestCase {

    let count = 10000

    func testWithStackView() {
        let myView = MyView1(frame: CGRect(x: 0, y: 0, width: 200, height: 50))
        myView.backgroundColor = .red

        let window = UIApplication.shared.keyWindow
        window?.addSubview(myView)

        for i in 0...count {
            myView.label.text = "\(i)"
            wait(for: [myExpectation!], timeout: 5)
        }

        myView.removeFromSuperview()
    }

    func testWithRegularConstraints() {
        let myView = MyView2(frame: CGRect(x: 0, y: 0, width: 200, height: 50))
        myView.backgroundColor = .red

        let window = UIApplication.shared.keyWindow
        window?.addSubview(myView)

        for i in 0...count {
            myView.label.text = "\(i)"
            wait(for: [myExpectation!], timeout: 5)
        }

        myView.removeFromSuperview()
    }

    func testWithManualLayout() {
        let myView = MyView3(frame: CGRect(x: 0, y: 0, width: 200, height: 50))
        myView.backgroundColor = .red

        let window = UIApplication.shared.keyWindow!
        window.addSubview(myView)

        for i in 0...count {
            myView.label.text = "\(i)"
            myView.setNeedsLayout()
            wait(for: [myExpectation!], timeout: 5)
        }

        myView.removeFromSuperview()
    }
}