Today’s example shows a static property providing the current date. Perfect mechanism when we don’t want to inject it everywhere where it’s used. How to test it? Check it out ⤵️ Initial setup let currentDateFormatter: DateFormatter = { let formatter = DateFormatter() formatter.dateStyle = .short formatter.timeStyle = .none return formatter }() var currentDateFormatted: String { currentDateFormatter.string(from: DateEnvironment.currentDate()) } enum DateEnvironment { static var currentDate: () -> Date = Date.init } extension Date { // 16.04.2025 static let sixteenthOfApril = Date(timeIntervalSince1970: 1744840515) } Old way - XCTest Override the static property in tests. Works, but not concurrency-safe (Ok, for XCTest because test ran serially). class CurrentDateFormatterTests: XCTestCase { func test_dateFormatting() { // ✅ DateEnvironment.currentDate = { .sixteenthOfApril } XCTAssertEqual(currentDateFormatted, "16.04.2025") } } Swift Testing before Swift 6.1 enum DateEnvironment { @TaskLocal static var currentDate: () -> Date = Date.init } struct CurrentDateFormatterTests { @Test func dateFormatting() { // ✅ DateEnvironment.$currentDate .withValue({ .sixteenthOfApril }) { #expect(currentDateFormatted == "16.04.2025") } } } Why @TaskLocal? ...

Mind your argument names in Swift Testing’s parametrised tests! As a follow up to my recent post on refactoring to use Swift Testing’s parametrised tests, I’m diving into the crucial - yet often overlooked topic of how to name your parametrised test inputs. Option 1: First Named Tuples Only the first tuple is named, all others rely on positional matching to (a, b, result). ✅ Minimal boilerplate for small input sets ❌ Readability drops after adding more cases ❌ Easy to mix up arguments position ❌ Hard to scan or extend func add(_ a: Int, _ b: Int) -> Int { a + b } ... @Test(arguments: [ (a: 1, b: 2, result: 3), (10, 15, 25), (1, -5, -4), (-1, -5, -6), (0, 0, 0), (1000, 1000, 2000), (10000, 50000, 60000), (-10, -3, -13) ]) func add_returnsCorrectSum(a: Int, b: Int, result: Int) { #expect(add(a, b) == result) } Option 2: Named Tuples Every tuple entry explicitly names all its fields (a: …, b: …, result: …) for all cases. ...

Intro Have you already started using Swift Testing instead of XCTest? I’m curious to see how you can refactor the test function (add_returnsCorrectSum) from the code snippet to use all powers of the Swift Testing framework. Could you explain what benefits does your refactored version has compared to my original code snippet? My approach In both approaches the test gives the same result. The point is the refactored version uses a Swift Testing parametrised test, and this makes a real difference. ...

Swift code refactor in action 👨🏻‍💻 Take a close look at the validate function. There’s a sneaky problem hidden in this code snippet. What will the function call return when passed nil? What problem is hidden here? First, the guard statement is redundant here. We can simplify the function to ⤵️ func validate(password: String?) -> Bool { password?.count ?? 0 > 8 } There’s no need to wrap password?.count ?? 0 in parentheses since the ?? operator already has higher precedence than >. ...

Paradigms Imperative In the imperative approach, we have a sequence of instructions that describe step by step how the program’s state is modified. Let’s look on the example ⤵️ var value = 0 func increment() { value += 1 // Mutating the state } print(value) // 0 increment() print(value) // 1 In the code we have a mutable variable value and a function increment that mutates the state (value). We first print the initial value, then increment it, and finally print the updated value. ...