🌤 SimpleWeatherApp

A minimal, production-grade SwiftUI demo that showcases how to architect for testability in Swift using the new Swift Testing Framework, @Mockable, and @Spyable. Built under the principles of Clean Architecture.

Published by Code with Shabib — codewithshabib.com

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🚀 Purpose

This project exists to:

• Demonstrate testable Clean Architecture in a real SwiftUI app
• Showcase how to use Mockable and Spyable for Swift-native test double generation
• Cover the entire spectrum of test doubles: mock, stub, spy, fake, and dummy
• Provide a reusable base for unit testing, SwiftUI previews, and architectural validation

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📝 Related Blog Post

This demo project is designed to complement the comprehensive blog post "Architecting for Testability in Swift: A Deep Dive into Mockable, Spyable, and the New Swift Testing Framework" - Read the full article.

The blog post provides:

• Detailed explanations of testing principles and strategies
• Cross-platform testing ecosystem analysis
• Organizational testing strategy guidance
• Future evolution of Swift testing
• Real-world examples and best practices

While this project serves as a practical implementation of those concepts, demonstrating:

• Clean Architecture in action
• Test double spectrum implementation
• SwiftUI preview strategies
• Unit testing patterns
• Integration testing approaches

Together, they provide a complete learning resource for modern Swift testing.

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🧱 Architecture Overview

This app uses strict layering:

SwiftUI View
    ↓
ViewModel (presentation logic)
    ↓
UseCase (domain logic)
    ↓
Repository (protocol)
    ↓
API Service (data layer)

Each layer depends only inward, aligned with Clean Architecture.

• DTOs: API-specific data structures
• Entities: Pure domain models
• ViewData: Presentation-layer structs mapped from domain models
• Mappers: Pure functions between layers (no mocking needed)

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📂 Project Structure

SimpleWeather/
├── WeatherView/
│   ├── Presentation/ (SwiftUI View, ViewModel, ViewData)
│   ├── Domain/ (Entities, Use Cases, Repository interfaces)
│   ├── Data/ (Repository impls, API services, DTOs)
│   └── Shared/ (Utilities, test doubles, etc.)
└── SimpleWeatherTests/
    └── Unit tests for all layers

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🧪 Testing Strategy

This project explicitly demonstrates all 5 types of test doubles:

Type	Used In	Example File(s) / Usage
✅ Dummy	DummyLogger, DummyAnalyticsTracker	WeatherView/Shared/Utilities/Dummies/ Used in previews and as default dependencies
✅ Stub	WeatherAPIServiceStub (configurable return values)	WeatherView/Data/Stubs/WeatherAPIServiceStub.swift Used in previews and tests
✅ Mock	MockWeatherRepositoryProtocol, MockFetchWeatherUseCaseProtocol (via Mockable)	Used in unit tests: SimpleWeatherTests/FetchWeatherUseCase.swift etc.
✅ Spy	AnalyticsTrackerSpy, LoggerSpy (via Spyable)	Used in unit tests: SimpleWeatherTests/WeatherViewModelTests.swift
✅ Fake	FakeWeatherAPIService (returns hardcoded but plausible data)	WeatherView/Data/Fakes/FakeWeatherAPIService.swift Used in previews and tests

Mocks and spies are generated using the Mockable and Spyable frameworks:

@mockable protocol FetchWeatherUseCaseProtocol { ... }
@spyable protocol AnalyticsTracker { ... }

Generated mocks/spies are shared between:

• ✅ Unit tests
• ✅ SwiftUI previews
• ✅ Integration-style flows

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🔍 Key Concepts in Code

• WeatherAPIService: talks to Open-Meteo
• WeatherRepository: translates DTO to domain
• FetchWeatherUseCase: business logic layer
• WeatherViewModel: testable, observable presentation logic
• Logger + AnalyticsTracker: abstracted observability
• FakeWeatherAPIService: replaces real API for local testing

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🧪 SwiftUI Preview with Test Doubles

Here's how to use stubs in SwiftUI previews:

// Using a stub with configurable return values
let stub = WeatherAPIServiceStub(
  weatherToReturn: WeatherResponseDTO(
    temperature: 28.0,
    condition: "Sunny"
  )
)
let repository = WeatherRepository(api: stub)
let useCase = FetchWeatherUseCase(repository: repository)
let viewModel = WeatherViewModel(
  fetchWeatherUseCase: useCase,
  logger: DummyLogger() // Using dummy for dependencies we don't care about
)
    
return WeatherView(viewModel: viewModel)

And here's how to use fakes for previews:

// Using a fake with fixed behavior
let fakeAPI = FakeWeatherAPIService()
let repository = WeatherRepository(api: fakeAPI)
let useCase = FetchWeatherUseCase(repository: repository)
let viewModel = WeatherViewModel(fetchWeatherUseCase: useCase)

// Fetch the weather when preview loads
Task {
  await viewModel.fetchWeather()
}

return WeatherView(viewModel: viewModel)

These approaches ensure UI previews can demonstrate different states without real networking.

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🧠 Why This Matters

Most Swift projects struggle with testability and architectural boundaries. This project demonstrates principles that you can adapt to your own architectural decisions:

• Apply dependency inversion principles strategically
• Create previewable, testable SwiftUI components
• Leverage code generation to reduce boilerplate

Understanding these patterns will help inform your own architectural decisions and testing strategies.

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🧪 Common Testing Patterns

This project demonstrates several testing patterns:

• Given-When-Then structure in all test cases
• Dependency injection via protocols for testability
• Arrange-Act-Assert pattern in test methods
• Verification of interactions via Mockable's verify() API
• Capturing arguments and return values for assertions
• Testing async/await code with the Swift Testing framework

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📋 Requirements

• iOS 18+
• Swift 6
• Xcode 16.3+
• Mockable framework
• Spyable framework

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🛠️ Getting Started

1. Clone this repository
2. Open SimpleWeather.xcodeproj in Xcode 16.3 or later
3. Build and run the project

To run the tests:

# From Xcode: Product > Test or ⌘U
# From command line:
xcodebuild test -scheme SimpleWeather -destination 'platform=iOS Simulator,name=iPhone 16'

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📱 App in Action

See the SimpleWeather app in action:

The demo shows the clean UI and weather fetching functionality in action, highlighting the architecture's simplicity and effectiveness.

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📄 License

This project is licensed under the MIT License - see the LICENSE file for details.