#include <iostream>
#include <cstring>
#include <algorithm>

using namespace std;

const int N = 100010;

int n, m;
int a[N], s1[N], s2[N];

int main()
{
    int T;
    scanf("%d", &T);
    while (T -- )
    {
        scanf("%d%d", &n, &m);
        for (int i = 1; i <= n; i ++ ) scanf("%d", &a[i]);
        a[ ++ n] = m;
        s1[n] = s2[n] = 0;
        for (int i = n - 1; i >= 0; i -- )
        {
            s1[i] = s1[i + 1], s2[i] = s2[i + 1];
            if (i % 2 == 0) s1[i] += a[i + 1] - a[i];
            else s2[i] += a[i + 1] - a[i];
        }

        int res = s1[0];
        for (int i = 0; i < n; i ++ )
        {
            int t = a[i + 1] - a[i];
            if (t == 1) continue;
            res = max(res, s1[0] - s1[i] + s2[i + 1] + t - 1);
        }
        printf("%d\n", res);
    }

    return 0;
}