Writing Multiple Test Cases Together

This lesson covers running multiple test cases together in C, so you understand the idea behind a batch of unit tests. It's for anyone searching "C unit test tutorial."

Testing multiple input patterns against a single function together is called a unit test. Preparing several cases ahead of time — a normal value, a boundary value, a special value — helps you find bugs faster.

The example bundles several test cases into three arrays, as, bs, and expected, loops through them one at a time passing each to the add() function, checking the result, and counting how many passed in passed.

A common early mistake is testing only the normal case and forgetting to check boundary values (like 0 or a negative number). It's important to include the easy-to-overlook cases in your tests too.

Real C development sometimes uses a dedicated testing framework like CUnit, but the underlying idea is exactly the same as what you're learning here.

📖 Reference code

#include <stdio.h>

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

int main(void) {
    int as[] = {2, -1, 0};
    int bs[] = {3, 1, 0};
    int expected[] = {5, 0, 0};
    int passed = 0;
    for (int i = 0; i < 3; i++) {
        int result = add(as[i], bs[i]);
        int ok = (result == expected[i]);
        if (ok) passed++;
        printf("Test %d: %s\n", i + 1, ok ? "OK" : "FAIL");
    }
    printf("%d/3 passed\n", passed);
    return 0;
}

✍️ Your code

Type your code, then press "Run"

🧪 This site can't compile or run 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).