Testing Async Code
Verify async/await flows reliably.
Testing Async Code is a free SwiftUI Academy lesson on CoddyKit — lesson 2 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the SwiftUI Academy learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.
Async Needs Special Care
Network calls and tasks finish later, not instantly. Your tests must wait for the result before asserting, or they check too early. ⏳
Mark the Test async
The simplest fix is an async test method. Swift lets you await directly, and the runner pauses until the work completes.
func testLoad() async {
}Await Your Method
Inside an async test you can use await just like real code. The line pauses until your ViewModel finishes loading.
await vm.load()Assert After Awaiting
Once the await returns, the data is ready. Now your assertion checks the final state, not an empty one. ✅
XCTAssertEqual(vm.items.count, 3)Throwing Async Tests
If the code can throw, mark the test throws too. Then try await lets errors bubble up and fail the test cleanly.
func testFetch() async throws {
try await vm.fetch()
}Avoid Real Networks
Hitting a live server makes tests slow and flaky. Inject a mock service that returns fixed data instead.
A Mock Service
A mock conforms to the same protocol but returns canned values. Your ViewModel cannot tell the difference, so the logic is tested honestly.
struct MockAPI: API {
func load() async -> [Item] { sample }
}Testing the Error Path
Make your mock throw on demand. Then you can verify the ViewModel sets an error state instead of crashing.
Expectations for Callbacks
For older callback APIs, use an XCTestExpectation. Fulfill it inside the callback, then wait so the test does not end early.
let exp = expectation(description: "done")Wait With a Timeout
Pair every expectation with a timeout. If the callback never fires, the test fails fast instead of hanging forever.
await fulfillment(of: [exp], timeout: 2)Prefer async Over Callbacks
When you can, write code with async/await. Tests stay short, linear, and far easier to read than nested callbacks.
Quick Check
How should you wait for async work in a modern XCTest?
Recap
You can now test async code: mark tests async, await results, mock the network, and use expectations for callbacks. Reliable every run. 🎉
Frequently asked questions
Is the “Testing Async Code” lesson free?
Yes — the full text of “Testing Async Code” is free to read here on the web, and the SwiftUI Academy course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the SwiftUI Academy course, upgrade to CoddyKit PRO.
What will I learn in “Testing Async Code”?
Verify async/await flows reliably. You practise SwiftUI Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start SwiftUI Academy?
No prior experience is required. SwiftUI Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 2 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “Testing Async Code” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this SwiftUI Academy lesson?
Yes. Every SwiftUI Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.