#include <bits/stdc++.h>
using namespace std;
using lli = long long int;
lli a[201] = {0};
int main() {
  lli tc, n, k, inp, cnt = 1, indi = 0;
  scanf("%lld", &tc);
  while (tc--) {
    indi = 0;
    cnt = 1;
    for (lli i = 1; i <= 200; i++) {
      a[i] = 0;
    }
    scanf("%lld", &n);
    scanf("%lld", &k);
    for (lli i = 1; i <= k; i++) {
      scanf("%lld", &inp);
      a[inp] = 1;
    }
    lli p = 1, q = 2;
    while (1) {
      indi = 0;
      for (lli i = 1; i <= n; i++) {
        if (a[i] == 0) {
          if (a[i + 1] == p && i + 1 <= n) {
            a[i] = q;
            indi = 1;
          }
          if (a[i - 1] == p && i - 1 >= 1) {
            a[i] = q;
            indi = 1;
          }
        }
      }
      if (indi == 1) cnt++;
      if (indi == 0) break;
      p++;
      q++;
    }
    cout << cnt << endl;
  }
  return 0;
}
