Testing async code in Swift - Mini Project: Build & Apply

Testing async code

📖 Scenario: You are building a simple Swift program that fetches a greeting message asynchronously, simulating a network call.

🎯 Goal: You will write code to test an asynchronous function that returns a greeting string after a short delay.

📋 What You'll Learn

Create an async function that returns a greeting string

Create a variable to hold the expected greeting

Write an async test function that calls the async greeting function

Print the result of the test to verify the greeting matches the expected value

💡 Why This Matters

🌍 Real World

Testing async code is important when working with network calls, file operations, or any tasks that take time to complete in real apps.

💼 Career

Many software jobs require writing and testing asynchronous code to ensure apps work smoothly without freezing or crashing.

1

Create the async greeting function

Create an async function called fetchGreeting() that returns a String. Inside, use try? await Task.sleep(nanoseconds: 1_000_000_000) to wait 1 second, then return the string "Hello, async world!".

Swift

# Create the async function fetchGreeting() that returns a String
# Your code here

Need a hint?

Use func fetchGreeting() async -> String to define the async function. Use try? await Task.sleep(nanoseconds: 1_000_000_000) to pause for 1 second.

2

Create the expected greeting variable

Create a constant called expectedGreeting and set it to the string "Hello, async world!".

Swift

func fetchGreeting() async -> String {
    try? await Task.sleep(nanoseconds: 1_000_000_000) // wait 1 second
    return "Hello, async world!"
}

# Create a constant expectedGreeting with the value "Hello, async world!"
# Your code here

Need a hint?

Use let expectedGreeting = "Hello, async world!" to create the constant.

3

Write the async test function

Write an async function called testFetchGreeting(). Inside, call fetchGreeting() with await and store the result in a variable called result. Then compare result with expectedGreeting using an if statement. If they match, print "Test passed", else print "Test failed".

Swift

func fetchGreeting() async -> String {
    try? await Task.sleep(nanoseconds: 1_000_000_000) // wait 1 second
    return "Hello, async world!"
}

let expectedGreeting = "Hello, async world!"

# Write an async function testFetchGreeting() to test fetchGreeting()
# Your code here

Need a hint?

Define func testFetchGreeting() async. Use let result = await fetchGreeting(). Use if result == expectedGreeting to check and print the test result.

4

Run the test and print the output

Call testFetchGreeting() inside a Task to run the async test. This will print either "Test passed" or "Test failed".

Swift

func fetchGreeting() async -> String {
    try? await Task.sleep(nanoseconds: 1_000_000_000) // wait 1 second
    return "Hello, async world!"
}

let expectedGreeting = "Hello, async world!"

func testFetchGreeting() async {
    let result = await fetchGreeting()
    if result == expectedGreeting {
        print("Test passed")
    } else {
        print("Test failed")
    }
}

# Run testFetchGreeting() inside a Task to print the test result
# Your code here

Need a hint?

Use Task { await testFetchGreeting() } to run the async test and print the result.