#include <bits/stdc++.h>
using namespace std;
#pragma GCC target("avx2")
#pragma GCC optimization("O3")
#pragma GCC optimization("unroll-loops")
template <typename Arg1>
void __f(const char* name, Arg1&& arg1) {
  cout << name << ": " << arg1 << std::endl;
}
template <typename Arg1, typename... Args>
void __f(const char* names, Arg1&& arg1, Args&&... args) {
  const char* comma = strchr(names + 1, ',');
  cout.write(names, comma - names) << " : " << arg1 << "| ";
  __f(comma + 1, args...);
}
const long long N = 2e5 + 10;
const long long mod = 1e9 + 7;
const long long INF = 1LL << 32;
long long n, k;
long long a[N];
pair<bool, long long> check(long long x) {
  vector<pair<long long, long long>> c;
  for (long long i = 1; i <= n; ++i) {
    c.emplace_back(a[i] - x, 0);
    c.emplace_back(a[i] + x, 1);
  }
  sort(c.begin(), c.end());
  long long cnt = 0;
  for (auto i : c) {
    if (i.second == 0)
      cnt++;
    else
      cnt--;
    if (cnt >= k) return {true, i.first};
  }
  return {false, -1};
}
void bs() {
  long long left = 0, right = 1e9 + 1;
  long long ans = -1;
  while (left <= right) {
    long long mid = (left + right) / 2;
    pair<bool, long long> hell = check(mid);
    if (hell.first) {
      ans = hell.second;
      right = mid - 1;
    } else {
      left = mid + 1;
    }
  }
  printf("%lld\n", ans);
}
void solve() {
  scanf("%lld%lld", &n, &k);
  k++;
  for (long long i = 1; i <= n; ++i) scanf("%lld", &a[i]);
  bs();
}
int32_t main() {
  long long t;
  cin >> t;
  while (t--) solve();
  return 0;
}
