#include <bits/stdc++.h>
using namespace std;
bool arr[201] = {0};
long long increment(long long start, long long end) {
  long long cnt = 0;
  bool initialarr[end];
  for (long long i = 0; i < end; i++) {
    initialarr[i] = arr[i];
  }
  for (long long i = start; i < end; i++) {
    if (initialarr[i]) {
      if (i - 1 >= 0) {
        if (initialarr[i - 1] == 0) {
          if (arr[i - 1] != 1) {
            arr[i - 1] = 1;
            cnt++;
          }
        }
      }
      if (i + 1 < end) {
        if (initialarr[i + 1] == 0) {
          if (arr[i + 1] != 1) {
            arr[i + 1] = 1;
            cnt++;
          }
        }
      }
    }
  }
  return cnt;
}
int32_t main() {
  long long t;
  cin >> t;
  while (t--) {
    long long n, k;
    cin >> n >> k;
    for (long long i = 0; i < n; i++) {
      arr[i] = 0;
    }
    long long count = k;
    long long x;
    for (long long i = 0; i < k; i++) {
      cin >> x;
      arr[x - 1] = 1;
    }
    long long t = 1;
    while (count < n) {
      count = count + increment(0, n);
      t++;
    }
    cout << t << "\n";
  }
  return 0;
}
