Mock interviews

How a mock works

1. TimedAbout 3 minutes a question, with a visible clock you can pause.
2. Out loudAnswer as you would in the room. Nothing is recorded.
3. Follow-upsThen the follow-up questions an interviewer would ask.
4. RubricTick the key points you covered; that is your score.

Mock sets (32)

• concurrency mock 1

  Concurrency · 5 questions · about 25 min

  • Sequential await vs async let
  • async let vs TaskGroup
  • Cooperative cancellation
  • Task {} vs Task.detached
  • What is an actor?

  Start this mock on the Concurrency page

• concurrency mock 2

  Concurrency · 5 questions · about 25 min

  • @MainActor view models
  • Reader-writer with a barrier vs an actor
  • Bridging callbacks with AsyncStream
  • Actor reentrancy: check, await, then act
  • Sendable and Swift 6 strict checking

  Start this mock on the Concurrency page

• concurrency mock 3

  Concurrency · 5 questions · about 25 min

  • Swift 6.2: default MainActor and @concurrent
  • Mutex vs actor
  • Single-flight token refresh
  • async/await vs completion handlers
  • Serial vs concurrent queues

  Start this mock on the Concurrency page

• swiftui mock 1

  SwiftUI · 5 questions · about 25 min

  • Which property wrapper for which data?
  • @StateObject vs @ObservedObject
  • @Observable model keeps resetting
  • @Observable vs ObservableObject
  • @Bindable for passed-in models

  Start this mock on the SwiftUI page

• swiftui mock 2

  SwiftUI · 5 questions · about 25 min

  • View identity: if/else vs a modifier
  • Why body runs often, and keeping it cheap
  • .task vs .onAppear + Task
  • .task(id:) and built-in debouncing
  • NavigationStack and deep links

  Start this mock on the SwiftUI page

• swiftui mock 3

  SwiftUI · 5 questions · about 25 min

  • Custom environment values with @Entry
  • .animation(_:value:) vs withAnimation
  • GeometryReader vs ViewThatFits and Layout
  • Loading and error state in SwiftUI
  • @ViewBuilder

  Start this mock on the SwiftUI page

• swiftui mock 4

  SwiftUI · 5 questions · about 25 min

  • UIViewRepresentable feedback loops
  • A timer that re-renders the whole screen
  • SwiftUI vs UIKit: key differences
  • @State vs a plain var
  • @Binding and the $ prefix

  Start this mock on the SwiftUI page

• swift-language mock 1

  Swift language · 5 questions · about 25 min

  • Closures and capture lists
  • Result and typed throws
  • inout parameters
  • Key paths
  • Opaque types (some) vs existentials (any)

  Start this mock on the Swift language page

• swift-language mock 2

  Swift language · 5 questions · about 25 min

  • @autoclosure
  • Copy-on-write
  • Property wrappers
  • Swift macros
  • Hashable

  Start this mock on the Swift language page

• swift-language mock 3

  Swift language · 5 questions · about 25 min

  • Associated types and primary associated types
  • Phantom types
  • Noncopyable types (~Copyable)
  • Optionals and why Swift has them
  • Value types vs reference types

  Start this mock on the Swift language page

• swift-language mock 4

  Swift language · 5 questions · about 25 min

  • Protocols vs abstract classes
  • @escaping vs non-escaping closures
  • Generics
  • Enums with associated and raw values
  • willSet and didSet

  Start this mock on the Swift language page

• memory-arc mock 1

  Memory & ARC · 5 questions · about 25 min

  • Retain cycles and how to break them
  • Retain cycles in closures
  • weak vs unowned
  • Autorelease pools today
  • Finding memory leaks

  Start this mock on the Memory & ARC page

• uikit mock 1

  UIKit · 5 questions · about 25 min

  • How Auto Layout works
  • Content hugging and compression resistance
  • Table and collection view cell reuse
  • UICollectionView vs UITableView and diffable data sources
  • UICollectionViewCompositionalLayout

  Start this mock on the UIKit page

• uikit mock 2

  UIKit · 5 questions · about 25 min

  • layoutSubviews
  • Hit-testing and the responder chain
  • Modal presentation styles
  • intrinsicContentSize
  • The UIViewController lifecycle

  Start this mock on the UIKit page

• networking mock 1

  Networking · 5 questions · about 25 min

  • Codable and mismatched keys
  • Retries with exponential backoff
  • App Transport Security (ATS)
  • A testable network layer
  • URLSessionConfiguration

  Start this mock on the Networking page

• networking mock 2

  Networking · 5 questions · about 25 min

  • Rate limits and temporary outages
  • Resilient large downloads
  • Reliable photo uploads
  • A fast image-loading pipeline
  • Making a network request

  Start this mock on the Networking page

• combine mock 1

  Combine · 5 questions · about 25 min

  • AnyCancellable and subscription lifetime
  • debounce vs throttle
  • combineLatest
  • merge vs zip
  • eraseToAnyPublisher

  Start this mock on the Combine page

• combine mock 2

  Combine · 5 questions · about 25 min

  • PassthroughSubject vs CurrentValueSubject
  • Testing Combine publishers
  • Combine vs async/await
  • Error handling in Combine
  • Preventing stale search results

  Start this mock on the Combine page

• persistence mock 1

  Persistence · 5 questions · about 25 min

  • Choosing the right storage
  • Storing secrets in the Keychain
  • The Core Data stack
  • SwiftData
  • Core Data and threading

  Start this mock on the Persistence page

• persistence mock 2

  Persistence · 5 questions · about 25 min

  • Rolling out a breaking schema change
  • Feature flags that change stored data
  • What to remove on logout
  • Using UserDefaults correctly
  • Reading and writing files

  Start this mock on the Persistence page

• architecture mock 1

  Architecture & patterns · 5 questions · about 25 min

  • MVVM done right
  • The observer pattern
  • Factory and builder patterns
  • Dependency injection
  • Strategy and command patterns

  Start this mock on the Architecture & patterns page

• testing mock 1

  Testing · 5 questions · about 25 min

  • Testing async code
  • Test doubles: stubs, spies, mocks and fakes
  • UI tests with XCUITest
  • Swift Testing
  • Debugging with LLDB

  Start this mock on the Testing page

• security mock 1

  Security · 5 questions · about 25 min

  • The pillars of iOS app security
  • Face ID and Touch ID done securely
  • Protecting API keys
  • Certificate and public key pinning
  • Jailbreak detection

  Start this mock on the Security page

• performance mock 1

  Performance · 5 questions · about 25 min

  • Profiling an iOS app
  • Dropped frames and hitches
  • Smooth scrolling in lists
  • Reducing app size
  • Offscreen rendering

  Start this mock on the Performance page

• performance mock 2

  Performance · 5 questions · about 25 min

  • Fixing a launch time regression
  • Measuring a slow screen without guessing
  • A 50,000-item list that stutters on updates
  • From a tap to a pixel on screen
  • Lazy loading

  Start this mock on the Performance page

• platform mock 1

  Platform & distribution · 5 questions · about 25 min

  • How push notifications are delivered
  • Background work with BGTaskScheduler
  • Region monitoring and geofencing
  • Code signing and provisioning profiles
  • Mixing Swift and Objective-C

  Start this mock on the Platform & distribution page

• platform mock 2

  Platform & distribution · 5 questions · about 25 min

  • KVC and KVO
  • Restoring navigation after the system kills the app
  • What an audio app must handle
  • Analytics that respect privacy
  • Reliable universal links

  Start this mock on the Platform & distribution page

• platform mock 3

  Platform & distribution · 5 questions · about 25 min

  • Routing a notification tap on cold start
  • Background sync without draining the battery
  • Fixing a location feature that drains the battery
  • Syncing a phone app and a watch app
  • App and scene lifecycle states

  Start this mock on the Platform & distribution page

• modern-platform mock 1

  Modern platform · 5 questions · about 25 min

  • Building widgets with WidgetKit
  • App Intents and Shortcuts
  • Live Activities
  • In-app purchases with StoreKit 2
  • Privacy manifests

  Start this mock on the Modern platform page

• accessibility-localization mock 1

  Accessibility & localization · 5 questions · about 25 min

  • Supporting VoiceOver
  • Supporting Dynamic Type
  • Localizing an iOS app
  • String Catalogs and plurals
  • Right-to-left languages

  Start this mock on the Accessibility & localization page

• system-design mock 1

  System design scenarios · 5 questions · about 25 min

  • Designing an infinite-scroll social feed
  • A thread-safe LRU cache
  • Offline-first architecture
  • A map with 10,000+ live pins
  • Responding to a crash spike

  Start this mock on the System design scenarios page

• system-design mock 2

  System design scenarios · 5 questions · about 25 min

  • An adaptive-bitrate player with Picture in Picture
  • A secure payment flow
  • A 60 fps short-video feed
  • A chat timeline that survives retries
  • A release that causes data loss

  Start this mock on the System design scenarios page