#include <bits/stdc++.h>
using namespace std;
const long long mod = 1e9 + 7;
int k[1000010];
long long qpow(long long x, int n) {
  long long ans = 1;
  for (; n; n >>= 1, x = x * x % mod)
    if (n & 1) ans = ans * x % mod;
  return ans;
}
long long lpow(long long x, int n) {
  long long ans = 1;
  for (; n; n >>= 1, x *= x) {
    if (n && x > mod) return mod;
    if (n & 1) ans *= x;
    if (ans > mod) return mod;
  }
  return ans;
}
int main() {
  int t;
  scanf("%d", &t);
  while (t--) {
    int n, p;
    scanf("%d%d", &n, &p);
    for (int i = 0; i < n; i++) scanf("%d", &k[i]);
    sort(k, k + n);
    long long d = 0;
    long long sl = 0, sr = 0, q = k[n - 1];
    for (int i = n - 1; i >= 0; i--) {
      if (q > k[i]) {
        sl = sl * qpow(p, q - k[i]) % mod;
        sr = sr * qpow(p, q - k[i]) % mod;
        d = min(d * lpow(p, q - k[i]), mod);
        q = k[i];
      }
      if (d)
        d--, sr++;
      else
        d++, sl++;
    }
    sl = sl * qpow(p, q) % mod;
    sr = sr * qpow(p, q) % mod;
    printf("%lld\n", (sl - sr + mod) % mod);
  }
}
