steipete

The Ultimate Swift Testing Playbook (2024 WWDC Edition, expanded with Apple docs from June 2025)

Updated with info from https://developer.apple.com/documentation/testing fetched via Firecrawl on June 7, 2025.

See also my blog: See also my blog post: https://steipete.me/posts/2025/migrating-700-tests-to-swift-testing

A hands-on, comprehensive guide for migrating from XCTest to Swift Testing and mastering the new framework. This playbook integrates the latest patterns and best practices from WWDC 2024 and official Apple documentation to make your tests more powerful, expressive, and maintainable.

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1. Migration & Tooling Baseline

ole

import SwiftUI

extension View {
    /// Proposes a percentage of its received proposed size to `self`.
    ///
    /// This modifier multiplies the proposed size it receives from its parent
    /// with the given factors for width and height.
    ///
    /// If the parent proposes `nil` or `.infinity` to us in any dimension,
    /// we’ll forward these values to our child view unchanged.

beesandbombs

float[][] result;
float t, c;

float ease(float p) {
  p = c01(p);
  return 3*p*p - 2*p*p*p;
}

float ease(float p, float g) {

jtrivedi

func scrollViewDidScroll(_ scrollView: UIScrollView) {
    for (i, view) in scrollView.subviews.enumerated() {
        var ty = 0.0
        if scrollView.contentOffset.y < 0 {
            // We're scrolling past the top of the scroll view.
            // Translate each item in the scroll view by some amount based on its index and scroll offset.
            ty = CGFloat(i) * abs(offsetY) / 8.0 * pow(1.12, CGFloat(i))
        }
        view.transform = CGAffineTransform(translationX: 0, y: ty)
    }

maximkrouk

// - Depends on https://github.com/capturecontext/swift-declarative-configuration
// - Depends on https://github.com/capturecontext/swift-foundation-extensions
//   - ⚠️ Resettable is moving to https://github.com/capturecontext/swift-resettable
// - Depends on https://gist.github.com/maximkrouk/942125396a857e49203ddb933d557c31

import UIKit
import FoundationExtensions
import DeclarativeConfiguration

fileprivate extension UIView {

keith

Usage

1. swiftc main.swift -emit-module-path main.swiftmodule -emit-executable -enable-private-imports -Xfrontend -enable-implicit-dynamic
2. ./main -> prints From original bar()
3. swiftc -emit-library inject.swift -o inject.dylib -I . -Xlinker -undefined -Xlinker suppress -Xlinker -flat_namespace -Xfrontend -disable-access-control
4. DYLD_INSERT_LIBRARIES=inject.dylib ./main -> prints From replacement bar()

Notes

• Passing -Xfrontend -enable-implicit-dynamic removes you from having to add dynamic to everything you want to be replacable

zntfdr

// Original article here: https://fivestars.blog/swiftui/swiftui-share-layout-information.html

import SwiftUI

extension View {
  func readSize(onChange: @escaping (CGSize) -> Void) -> some View {
    background(
      GeometryReader { geometryProxy in
        Color.clear
          .preference(key: SizePreferenceKey.self, value: geometryProxy.size)

IanKeen

extension Publisher {
    func asResult() -> AnyPublisher<Result<Output, Failure>, Never> {
        return map(Result.success)
            .catch { Just(Result.failure($0)) }
            .eraseToAnyPublisher()
    }
}

extension Publisher {
    func values<S, F: Error>() -> AnyPublisher<S, Never> where Output == Result<S, F>, Failure == Never {

RuiAAPeres

import ReactiveSwift
import XCTest

private let counterFailure: (Int, Int) -> String = { count, maxCount in
  return "Counter is currently at \(count) which higher than the max \(maxCount)"
}

private let timeoutFailure = "Expectation timeout"

private let infoTemplate: (String, String, Int) -> String = { fileName, functionName, lineNumber in

wotjd

import SwiftUI

// https://medium.com/@lyeskinnikitaalexandrovich/mastering-xcode-previews-with-snapkit-uikit-aa82a146059a
enum DebugPreviewLayout {
  case fitWidth(CGFloat)
  case fitHeight(CGFloat)
  case `default`
}

final class DebugPreviewLayoutView: UIView {