#include <bits/stdc++.h>
using namespace std;
const long long BIG_INF = 4e18;
const long long INF = 2e9;
const long long mod = 1e9 + 7;
long long fast_exp(long long a, long long b) {
  if (b <= 0)
    return 1;
  else {
    long long res = 1;
    res = fast_exp(a, b / 2);
    res = res % mod;
    res = (res * res) % mod;
    if (b % 2 == 1) res = (res * a) % mod;
    return res;
  }
}
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
long long true_rand(long long n) {
  uniform_int_distribution<long long> uid(0, n - 1);
  return uid(rng);
}
const long long N = 5e5 + 1000;
const long double pi = acos(-1.0);
using cd = complex<double>;
const double PI = acos(-1);
double eps = 1e-12;
string s, t;
int dp[2005][2005] = {};
int done[2005][2005] = {};
int frqs[2005][26] = {};
int frqt[2005][26] = {};
int moves_needed(int ptrs, int ptrt) {
  if (ptrs == -1 || ptrt == -1) {
    return abs(max(ptrs, ptrt) + 1);
  }
  if (done[ptrs][ptrt] == 1) return dp[ptrs][ptrt];
  int ans = INF;
  if (s[ptrs] == t[ptrt]) {
    ans = min(ans, moves_needed(ptrs - 1, ptrt - 1));
  } else {
    if (frqs[ptrs + 1][t[ptrt] - 'a'] - frqt[ptrt + 1][t[ptrt] - 'a'] > 0)
      ans = min(ans, moves_needed(ptrs, ptrt - 1) + 1);
    ans = min(ans, moves_needed(ptrs - 1, ptrt));
  }
  done[ptrs][ptrt] = 1;
  dp[ptrs][ptrt] = ans;
  return dp[ptrs][ptrt];
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  int tc;
  cin >> tc;
  while (tc--) {
    int n;
    cin >> n;
    for (int i = 0; i < n + 4; i++) {
      for (int j = 0; j < n + 4; j++) {
        dp[i][j] = INF;
        done[i][j] = 0;
      }
      for (int j = 0; j < 26; j++) {
        frqs[i][j] = 0;
        frqt[i][j] = 0;
      }
    }
    cin >> s;
    cin >> t;
    for (int i = n - 1; i >= 0; i--) {
      for (int ch = 0; ch < 26; ch++) {
        int add = 0;
        if (s[i] - 'a' == ch) add = 1;
        frqs[i][ch] = frqs[i + 1][ch] + add;
      }
      for (int ch = 0; ch < 26; ch++) {
        int add = 0;
        if (t[i] - 'a' == ch) add = 1;
        frqt[i][ch] = frqt[i + 1][ch] + add;
      }
    }
    int chk = 1;
    for (int i = 0; i < 26; i++) {
      if (frqs[0][i] != frqt[0][i]) chk = 0;
    }
    if (chk == 1)
      cout << moves_needed(n - 1, n - 1) << '\n';
    else
      cout << -1 << endl;
  }
  return 0;
}
