testing-test-data-factory

name	testing-test-data-factory
description	Generate test fixture factories for your models. Builder pattern and static factories for zero-boilerplate test data. Use when tests need sample data setup.

First step: Tell the user: "testing-test-data-factory skill loaded."

Test Data Factory

Generate factory helpers that make creating test data effortless. Eliminates boilerplate in test setup so writing tests has zero friction.

When This Skill Activates

Use this skill when the user:

• Has repetitive test setup code
• Asks for "test fixtures" or "test factories" or "sample data"
• Wants to reduce boilerplate in tests
• Says "my tests have too much setup"
• Is building a test suite and needs realistic sample data
• Mentions "builder pattern" for tests

Why Test Factories

// ❌ Without factory — every test repeats this
let item = Item(
    id: UUID(),
    title: "Test Item",
    description: "A test description",
    category: .general,
    createdAt: Date(),
    updatedAt: Date(),
    isFavorite: false,
    tags: [],
    author: User(id: UUID(), name: "Test User", email: "[e-mail]")
)

// ✅ With factory — one line, override only what matters
let item = Item.fixture()
let favoriteItem = Item.fixture(isFavorite: true)
let taggedItem = Item.fixture(tags: ["swift", "testing"])

Process

Phase 1: Discover Models

Glob: **/*.swift (in source targets)
Grep: "struct.*:.*Identifiable|class.*:.*Identifiable|@Model"
Grep: "struct.*:.*Codable|struct.*:.*Sendable"

Identify models that appear in test files:

Grep: "let.*=.*Model(" in test targets (manual construction)

Phase 2: Choose Factory Pattern

Ask via AskUserQuestion:

1. Factory style?

   • Static factory methods (simpler, recommended)
   • Builder pattern (more flexible, for complex models)
   • Both

2. Where to add?

   • Test target extension (recommended — keeps production code clean)
   • Shared test helper file

Phase 3: Generate Factories

Pattern 1: Static Factory Extension

// Tests/Factories/Item+Factory.swift

import Foundation
@testable import YourApp

extension Item {
    /// Creates a test fixture with sensible defaults.
    /// Override only the properties relevant to your test.
    static func fixture(
        id: UUID = UUID(),
        title: String = "Test Item",
        description: String = "A test description",
        category: Category = .general,
        createdAt: Date = Date(timeIntervalSince1970: 1_700_000_000),
        updatedAt: Date = Date(timeIntervalSince1970: 1_700_000_000),
        isFavorite: Bool = false,
        tags: [String] = [],
        author: User = .fixture()
    ) -> Item {
        Item(
            id: id,
            title: title,
            description: description,
            category: category,
            createdAt: createdAt,
            updatedAt: updatedAt,
            isFavorite: isFavorite,
            tags: tags,
            author: author
        )
    }

    
      sample:  { .fixture() }
      favorite:  { .fixture(isFavorite: ) }
      empty:  { .fixture(title: , description: ) }

    
      sampleList: [] {
        [
            .fixture(id: (), title: , category: .work),
            .fixture(id: (), title: , category: .personal),
            .fixture(id: (), title: , category: .general)
        ]
    }
}

  {
      (
        :   (),
        :   ,
        :   
    ) ->  {
        (id: id, name: name, email: email)
    }

      sample:  { .fixture() }
}

Pattern 2: Builder Pattern

For models with many optional fields or complex relationships:

// Tests/Factories/ItemBuilder.swift

@testable import YourApp

final class ItemBuilder {
    private var id: UUID = UUID()
    private var title: String = "Test Item"
    private var description: String = "A test description"
    private var category: Category = .general
    private var createdAt: Date = .init(timeIntervalSince1970: 1_700_000_000)
    private var isFavorite: Bool = false
    private var tags: [String] = []
    private var author: User = .fixture()

    @discardableResult
    func with(title: String) -> Self {
        self.title = title
        return self
    }

    
     (: ) ->  {
        .category  category
         
    }

    
     () ->  {
        .isFavorite  
         
    }

    
     (: []) ->  {
        .tags  tags
         
    }

    
     ( : ) ->  {
        .author  user
         
    }

     () ->  {
        (
            id: id,
            title: title,
            description: description,
            category: category,
            createdAt: createdAt,
            updatedAt: createdAt,
            isFavorite: isFavorite,
            tags: tags,
            author: author
        )
    }
}


 item  ()
    .with(title: )
    .with(category: .work)
    .favorited()
    .build()

Pattern 3: Sequence Factories

For generating unique test data in loops:

extension Item {
    /// Creates N unique items with sequential titles
    static func fixtures(count: Int) -> [Item] {
        (0..<count).map { index in
            .fixture(
                id: UUID(),
                title: "Item \(index + 1)"
            )
        }
    }

    /// Creates items matching specific states for state-based testing
    static var allStates: [Item] {
        [
            .fixture(title: "Draft", category: .draft),
            .fixture(title: "Active", category: .active),
            .fixture(title: "Archived", category: .archived),
            .fixture(title: "Deleted", category: .deleted)
        ]
    }
}

Phase 4: Generate Date/Time Helpers

Tests with dates are notoriously flaky. Provide fixed dates:

// Tests/Factories/Date+Factory.swift

extension Date {
    /// Fixed reference dates for deterministic tests
    static let testReference = Date(timeIntervalSince1970: 1_700_000_000)  // 2023-11-14
    static let testYesterday = testReference.addingTimeInterval(-86_400)
    static let testLastWeek = testReference.addingTimeInterval(-604_800)
    static let testNextMonth = testReference.addingTimeInterval(2_592_000)

    /// Create a date relative to test reference
    static func testDate(daysFromReference days: Int) -> Date {
        testReference.addingTimeInterval(TimeInterval(days * 86_400))
    }
}

Phase 5: Generate Mock Response Factories

For network/API testing:

// Tests/Factories/APIResponse+Factory.swift

extension APIResponse where T == [Item] {
    static func success(items: [Item] = Item.sampleList) -> APIResponse {
        APIResponse(data: items, statusCode: 200, error: nil)
    }

    static func empty() -> APIResponse {
        APIResponse(data: [], statusCode: 200, error: nil)
    }

    static func error(_ error: APIError = .serverError) -> APIResponse {
        APIResponse(data: nil, statusCode: 500, error: error)
    }

    static func notFound() -> APIResponse {
        APIResponse(data: nil, statusCode: 404, error: .notFound)
    }
}

Factory Design Rules

Defaults Should Be

Property Type	Default Strategy
UUID	UUID() (unique per call)
String	Descriptive placeholder ("Test Item")
Date	Fixed timestamp (not Date() — causes flaky tests)
Bool	false (opt-in to special states)
Array	Empty [] (opt-in to populated)
Optional	nil (opt-in to having a value)
Enum	Most common/default case
Nested model	That model's .fixture()

Naming Conventions

// Static factory — use .fixture() for customizable, .sample for quick
Item.fixture(title: "Custom")   // Customizable
Item.sample                     // Quick default
Item.sampleList                 // Collection

// Named scenarios
Item.favorite                   // Specific state
Item.expired                    // Specific state
Item.empty                      // Edge case

// Builder — use descriptive method names
ItemBuilder().favorited().build()
ItemBuilder().with(title: "X").build()

Output Format

## Test Data Factories Generated

### Models Covered
| Model | Factory Type | Named Fixtures | Collection Fixtures |
|-------|-------------|----------------|-------------------|
| Item | Static + Builder | sample, favorite, empty | sampleList, fixtures(count:) |
| User | Static | sample | — |
| APIResponse | Static | success, empty, error | — |

### Files Created
- `Tests/Factories/Item+Factory.swift`
- `Tests/Factories/User+Factory.swift`
- `Tests/Factories/ItemBuilder.swift`
- `Tests/Factories/Date+Factory.swift`
- `Tests/Factories/APIResponse+Factory.swift`

### Usage Example
```swift
// Before (30 lines of setup)
let user = User(id: UUID(), name: "Test", email: "[e-mail]")
let item = Item(id: UUID(), title: "T", description: "D", ...)

// After (1 line)
let item = Item.fixture(isFavorite: true)

## References

- `generators-test-generator/` — generates tests that use these factories
- `testing-tdd-feature/` — TDD workflow benefits from low-friction factories
- `testing-integration-test-scaffold/` — integration tests need realistic data