Effective UI Testing in iOS: Utilizing Launch Arguments
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Chapter 1: Introduction to UI Testing with Launch Arguments
Difficulty Level: Beginner | Easy | Normal | Challenging
This guide is crafted using Xcode 15.0 and Swift 5.9.
Terminology:
- Launch Arguments: These are command-line parameters provided to an app during startup, allowing developers to modify app behavior for debugging and testing purposes.
Section 1.1: Understanding the Context
Here’s how to tackle this common issue effectively.
Section 1.2: Implementing the Solution
To manage different configurations for testing and production environments, we utilize a selector that determines whether we’re using a mock network client for testing or a production-ready client.
struct NetworkClientSelector {
static func select() -> NetworkClientConfiguration {
#if DEBUG
if ProcessInfo.processInfo.arguments.contains("-UITests") {
return DebugNetworkClientConfiguration()}
#endif
return ReleaseNetworkClientConfiguration()
}
}
The NetworkClientConfiguration can be simple, allowing the choice between MockNetworkClient and MainNetworkClient.
protocol NetworkClientConfiguration {
var networkClient: NetworkClient { get }
}
struct DebugNetworkClientConfiguration: NetworkClientConfiguration {
var networkClient: NetworkClient {
MockNetworkClient()}
}
struct ReleaseNetworkClientConfiguration: NetworkClientConfiguration {
var networkClient: NetworkClient {
MainNetworkClient()}
}
Section 1.3: Mock Network Client Implementation
Here’s a simplified version of the MockNetworkClient. Ideally, this would reside in a framework accessible to both the tests and the main project.
import Foundation
import NetworkClient
final class MockNetworkClient: NetworkClient {
var fetchAsyncResult: Any?
var fetchCompletionResult: APIResponse?
private(set) var fetchAsyncCalled = false
private(set) var fetchCompletionCalled = false
func fetch(
api: URLGenerator,
method: HTTPMethod,
request: T
) async throws -> T.ResponseDataType? where T: APIRequest {
fetchAsyncCalled = true
if let error = try (fetchAsyncResult as? APIResponse)?.result.get() {
throw error}
if let result = fetchAsyncResult as? T.ResponseDataType {
return result}
switch api.url {
case API.users.url:
return mockUsers() as? T.ResponseDataTypedefault:
return nil}
}
private func mockUsers() -> [UserDTO] {
[
UserDTO(id: 1, username: "Username One"),
UserDTO(id: 2, username: "Username Two")
]
}
}
Section 1.4: Main Network Client Overview
The implementation of MainNetworkClient is crucial for clarity, so here’s a brief overview:
import Foundation
public final class MainNetworkClient: NetworkClient {
private let urlSession: URLSession
public init(urlSession: URLSession = .shared) {
self.urlSession = urlSession}
public func fetch(
api: URLGenerator,
method: HTTPMethod,
request: T
) async throws -> T.ResponseDataType? {
let urlRequest = try createURLRequest(api: api, method: method, request: request)
let (data, response) = try await urlSession.data(for: urlRequest)
let httpResponse = try self.handleResponse(data, response)
try handleStatusCode(statusCode: httpResponse.statusCode)
return httpResponse.statusCode == 204 ? nil : try parseData(data, for: request)
}
// Additional methods omitted for brevity...
}
Section 1.5: Enabling UI Tests
To activate the mock data for UI tests, set the launch arguments as follows:
app.launchArguments = ["-UITests"]
This sets up the environment for the following test:
import XCTest
final class NetworkClientSwitcherUITests: XCTestCase {
let app = XCUIApplication()
override func setUpWithError() throws {
continueAfterFailure = false
app.launchArguments = ["-UITests"]
app.launch()
}
func testUserListLoads() throws {
XCTAssertTrue(app.staticTexts["Username One"].exists)
XCTAssertTrue(app.staticTexts["Username Two"].exists)
}
}
Chapter 2: Additional Testing Strategies
While utilizing launch arguments for UI testing simplifies simulating various application states, exploring alternatives can also enhance the flexibility of your testing framework. Environment variables, for example, can control app behavior during tests similarly and can be used alongside or instead of launch arguments.
The first video titled "UI Testing a SwiftUI application in Xcode | Advanced Learning #18" provides insights into advanced techniques for UI testing in SwiftUI applications.
The second video, "UI Testing Tutorial with SwiftUI and macOS - Xcode 16," covers a comprehensive tutorial on UI testing using SwiftUI in Xcode.
Conclusion
Mastering launch arguments for UI testing in iOS is a significant advancement towards establishing reliable, efficient, and independent tests. By isolating tests from live backend systems, we gain control over the testing environment and ensure robustness against external changes. The methods discussed here—from configuring MockNetworkClient for UI tests to adjusting schemes for various testing scenarios—offer a strong foundation for iOS developers aiming to enhance their testing strategies.