When running a bucket sort program using UnitTestBotCpp, it cannot generate test cases

[JeffreyWu]

When running a bucket sort program using UnitTestBotCpp, which is not a complex program, I am unable to generate the corresponding test cases. Why is this happening?
Here is the code:
void bucketSort(std::vector& arr) {
int n = arr.size();
int maxVal = *std::max_element(arr.begin(), arr.end());
int minVal = *std::min_element(arr.begin(), arr.end());
int bucketSize = (maxVal - minVal) / n + 1;

std::vector<std::vector<int>> buckets(n);

for (int num : arr) {
    int bucketIndex = (num - minVal) / bucketSize;
    buckets[bucketIndex].push_back(num);
}

for (std::vector<int>& bucket : buckets) {
    std::sort(bucket.begin(), bucket.end());
}

int index = 0;
for (std::vector<int>& bucket : buckets) {
    for (int num : bucket) {
        arr[index++] = num;
    }
}

}