How to Use Combinations of Sets as Test Data for Effective Unit Testing

Unit testing is an essential practice in software development, ensuring that your code behaves as expected under various conditions. When testing functions that rely on numerical inputs—such as one that determines if three lengths can form a valid triangle—you must consider both typical and fringe cases. This blog post guides you through generating and using combinations of sets as test data, ensuring a thorough evaluation of your function.

Understanding the Problem

When testing a function that checks if three lengths can form a triangle, you need a diverse set of test cases. This includes:

• Normal Values: Typical lengths (e.g., 5, 10, 5).
• Edge Cases: Values that challenge the algorithm, such as:
  • Negative numbers (e.g., -1, 0).
  • Very large numbers that might cause overflow (e.g., 1000, inf).
  • Values at the boundary of valid inputs.

Here’s an example of input sets you might use:

(inf, 0, -1), (5, 10, 1000), (10, 5, 5), (0, -1, 5), (1000, inf, inf)

The challenge is generating combinations of these values—both with and without repetition. Let’s look at how to tackle this problem effectively.

Generating Combinations of Sets

To generate combinations from a set of values, you could implement it in various programming languages. Below, I’ll share a method using C, which allows you to compute combinations in a precise manner.

Algorithm Implementation in C

In the spirit of mathematical algorithms, we can refer to “Algorithm 515”, as presented by Buckles and Lybanon. The following C function will help generate the xth lexicographically ordered set of p elements from n:

void combination(int* c, int n, int p, int x) {
    int i, r, k = 0;
    for(i = 0; i < p - 1; i++) {
        c[i] = (i != 0) ? c[i - 1] : 0;
        do {
            c[i]++;
            r = choose(n - c[i], p - (i + 1)); // Helper function needed
            k = k + r;
        } while(k < x);
        k = k - r;
    }
    c[p - 1] = c[p - 2] + x - k;
}

Explanation of the Code

• Function Input: The function receives an array c where combinations will be stored, the total number of elements n, the number of elements to combine p, and the specific combination index x to produce.
• Outer Loop: The outer loop iterates to fill p - 1 elements of the combination.
• Inner Loop: This uses a do-while loop to increment the combination until the required xth set is found.

Getting the Helper Function

You’ll need a choose function to calculate combinations of n taken k at a time:

int choose(int n, int k) {
    if (k > n || k < 0) return 0;
    if (k == 0 || k == n) return 1;
    if (k == 1) return n;

    int r = 1;
    for (int i = 1; i <= k; i++) {
        r = r * (n - i + 1) / i;
    }
    return r;
}

Conclusion

Testing functions with combinations of numerical sets can vastly improve the reliability of your software. By generating diverse test cases, you can ensure your code can handle unexpected inputs.

If you have questions or suggestions about implementing testing strategies, feel free to share your thoughts in the comments. Together, we can make software development more robust!