Swift Testing

This skill covers the modern Swift Testing framework introduced in Swift 5.9 for writing clean, expressive tests.

Overview

Swift Testing is Apple’s modern testing framework that provides a more expressive and flexible way to write tests compared to XCTest. It features Swift-native syntax, parameterized tests, and better async support.

Available References

• Test Basics – Test declarations, assertions, and lifecycle
• Async Testing – Testing async/await code
• Parameterized Tests – Running tests with multiple inputs
• Test Organization – Suites, tags, and test structure

Quick Reference

Basic Test

import Testing

@Test
func addition() {
    let result = 1 + 1
    #expect(result == 2)
}

@Test
func throwsError() throws {
    #expect(throws: MyError.invalid) {
        try riskyOperation()
    }
}

Async Test

@Test
func fetchData() async throws {
    let data = try await fetchUser()
    #expect(data.name == "Ada")
}

Parameterized Test

@Test(arguments: ["hello", "world", "swift"])
func stringLength(string: String) {
    #expect(string.count > 0)
}

@Test(arguments: zip([1, 2, 3], [1, 4, 9]))
func squared(input: Int, expected: Int) {
    #expect(input * input == expected)
}

Test Suite

@Suite
struct CalculatorTests {
    let calculator = Calculator()
    
    @Test
    func add() {
        #expect(calculator.add(2, 3) == 5)
    }
    
    @Test
    func subtract() {
        #expect(calculator.subtract(5, 3) == 2)
    }
}

Swift Testing vs XCTest

Best Practices

1. Use descriptive names – Test names should explain behavior
2. Test one thing – Each test should verify one concept
3. Use #require for preconditions – Fail fast if setup fails
4. Leverage parameterized tests – Test multiple inputs efficiently
5. Organize with suites – Group related tests
6. Use tags – Categorize tests for selective running
7. Test async code – Use async test functions
8. Keep tests independent – No shared state between tests

Running Tests

# Run all tests
swift test

# Run specific test
swift test --filter addition

# Run tests by tag
swift test --tag unit

# Run with verbose output
swift test --verbose

For More Information

Visit https://swiftzilla.dev for comprehensive Swift Testing documentation.