Checking correctness (a first step towards testing)

This lesson covers writing a simple test in Objective-C, with the aim of taking the first step towards checking your program is correct.

You learn the basic idea of test code: confirming with an if statement whether a condition came out as expected. Checking automatically that a function's result is right saves you doing it by hand every time.

The sample code checks with an if statement whether add(2, 3) gives 5, printing a pass or a fail accordingly. It gives you a feel for confirming a result in code rather than by eye.

A common early stumble is checking behaviour by hand every time and missing something. In practice you would use a dedicated framework (such as XCTest), but the underlying idea is the same.

Remember too that an assertion is a development-time debugging aid, not a substitute for real error handling in production.

📖 Reference code

NSInteger add(NSInteger a, NSInteger b) {
    return a + b;
}

if (add(2, 3) == 5) {
    NSLog(@"Test passed: add(2, 3) is 5");
} else {
    NSLog(@"Test failed");
}
NSLog(@"Test run complete");

✍️ Your code

Type your code, then press "Run"

🧪 This site can't compile or run Objective-C directly, so it checks on the spot whether what you typed matches the reference code (scoring happens entirely in your browser — nothing is sent anywhere).