Swift Testing

Overview

New unit and integration tests use Swift Testing (import Testing). Existing Quick + Nimble specs (*Spec.swift) are retained as-is and migrated only on request.

Framework	File suffix	Location
Swift Testing	*Tests.swift	Tests/Sources/ mirroring production path
Quick + Nimble	*Spec.swift	Tests/Sources/Specs/

File Placement

Mirror the production source path for the module under test:

Module	Test directory
App	{PROJECT_NAME}Tests/Sources/
Data	Modules/Data/Tests/Sources/
Domain	Modules/Domain/Tests/Sources/
Model	Modules/Model/Tests/Sources/

Naming Conventions

Element	Convention	Example
File	<TypeUnderTest>Tests.swift	DefaultFeatureFlagRepositoryTests.swift
Suite type	<TypeUnderTest>Tests	struct DefaultFeatureFlagRepositoryTests
Suite display name	@Suite("<TypeUnderTest>")	@Suite("DefaultFeatureFlagRepository")
Test display name	@Test("lowercase behavior sentence")	@Test("falls back to the flag default value")
Test function	camelCase matching display name	func fallsBackToTheFlagDefaultValue()

Minimal Example

import Testing

@testable import Data
import Domain

@Suite("DefaultRemoteConfigRepository")
struct DefaultRemoteConfigRepositoryTests {

    @Test("returns a typed stored value")
    func returnsATypedStoredValue() async {
        let key = RemoteConfigKey(name: "feature_enabled", defaultValue: false)
        let repository = DefaultRemoteConfigRepository(
            source: StubRemoteConfigSource(values: [key.name: .string("true")])
        )

        let value = await repository.value(for: key)

        #expect(value == true)
    }
}

private actor StubRemoteConfigSource: RemoteConfigSource {
    private let values: [String: RemoteConfigStoredValue]
    init(values: [String: RemoteConfigStoredValue] = [:]) { self.values = values }
    func refresh() async throws {}
    func value(forKey key: String) async -> RemoteConfigStoredValue? { values[key] }
}

Key Rules

• Use #expect by default; use #require only when subsequent lines depend on a non-nil or non-throwing prerequisite.
• Prefer struct suites — each test gets a fresh instance, preventing shared state.
• Use init() for setup; deinit on a class suite for teardown (rare).
• Tests run in parallel by default. Mark a suite .serialized only when it accesses global state (e.g. NetworkStubber).
• No real network calls — use NetworkStubber (OHHTTPStubs) or inline protocol stubs.
• Use actor stubs when the protocol has async members or mutable state; use struct otherwise.

AI Skill

The /swift-testing Claude Code skill provides detailed references for assertions, traits, parameterized tests, async testing, test doubles, and Quick + Nimble migration:

skills/swift-testing/
├── SKILL.md
└── references/
    ├── fundamentals.md
    ├── expectations.md
    ├── traits-and-tags.md
    ├── parameterized-testing.md
    ├── async-testing.md
    ├── test-doubles.md
    └── migration-from-quick-nimble.md