This content originally appeared on Level Up Coding - Medium and was authored by Bharat Lal Verma
Test-Driven-Development (TDD) is a software development approach where tests are written before the actual code. This methodology ensures that the code is thoroughly tested and meets the desired requirements. In iOS development, TDD can lead to more robust and maintainable applications.
Understanding TDD
The TDD cycle consists of three main steps:
- Red: Write a test that fails because the functionality isn’t implemented yet.
- Green: Write the minimal amount of code to make the test pass.
- Refactor: Clean up the code, ensuring it adheres to best practices and is maintainable.
This cycle is repeated for each new feature or bug fix, ensuring continuous integration of tested code.
Implementing TDD in iOS
Let’s consider a scenario where we need to fetch a list of repositories from GitHub. We’ll use TDD to develop this feature.
- Red: Write a failing test for fetching repositories.
import XCTest
@testable import YourApp
class RepositoryServiceTests: XCTestCase {
func testFetchRepositories() async throws {
let service = RepositoryService()
let repositories = try await service.fetchRepositories()
XCTAssertEqual(repositories.count, expectedCount)
}
}
This test will fail initially because the fetchRepositories method isn't implemented.
2. Green: Implement the minimal code to make the test pass.
import Foundation
struct Repository: Decodable {
let id: Int
let name: String
}
class RepositoryService {
func fetchRepositories() async throws -> [Repository] {
let url = URL(string: "https://api.github.com/users/username/repos")!
let (data, _) = try await URLSession.shared.data(from: url)
let repositories = try JSONDecoder().decode([Repository].self, from: data)
return repositories
}
}
Now, the test should pass as the fetchRepositories method returns the expected data.
3. Refactor: Clean up the code.
- Error Handling: Ensure the method handles possible errors gracefully.
- Dependency Injection: Inject URLSession to make the code more testable.
import Foundation
enum RepositoryServiceError: Error {
case invalidURL
case requestFailed
case decodingFailed
}
protocol URLSessionProtocol {
func data(from url: URL) async throws -> (Data, URLResponse)
}
extension URLSession: URLSessionProtocol {}
class RepositoryService {
private let session: URLSessionProtocol
init(session: URLSessionProtocol = URLSession.shared) {
self.session = session
}
func fetchRepositories() async throws -> [Repository] {
guard let url = URL(string: "https://api.github.com/users/username/repos") else {
throw RepositoryServiceError.invalidURL
}
let (data, response) = try await session.data(from: url)
guard (response as? HTTPURLResponse)?.statusCode == 200 else {
throw RepositoryServiceError.requestFailed
}
do {
let repositories = try JSONDecoder().decode([Repository].self, from: data)
return repositories
} catch {
throw RepositoryServiceError.decodingFailed
}
}
}
By injecting URLSession, we can mock network responses in our tests, making them more reliable and faster.
Benefits of TDD in iOS Development
- Improved Code Quality: Writing tests first ensures that the code meets the requirements and handles edge cases.
- Refactoring Confidence: With a comprehensive test suite, developers can refactor code without fear of introducing bugs.
- Documentation: Tests serve as documentation, providing insights into the code’s functionality.
Conclusion
Adopting TDD in iOS development leads to more reliable and maintainable applications. By following the Red-Green-Refactor cycle, developers can ensure that their code is robust and meets the desired requirements.
Note: Replace "https://api.github.com/users/username/repos" with the actual GitHub API URL relevant to your application.
I added an example app that loads users’ public repositories from GitHub and shows them in a List. Check out it on GitHub.
GitHub - bharatlal087/tdd-ios: TDD - Test Driven Development
Test-Driven-Development (TDD) in iOS was originally published in Level Up Coding on Medium, where people are continuing the conversation by highlighting and responding to this story.
This content originally appeared on Level Up Coding - Medium and was authored by Bharat Lal Verma
Bharat Lal Verma | Sciencx (2025-02-24T13:41:51+00:00) Test-Driven-Development (TDD) in iOS. Retrieved from https://www.scien.cx/2025/02/24/test-driven-development-tdd-in-ios/
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