#include <bits/stdc++.h>
using namespace std;
const int N = 2e3 + 7;
const int inf = 1e9 + 7;
int T, n, dp[N][N], cnt[N], qzs[N][26], qzt[N][26];
char s[N], t[N];
void Min(int &x, int y) {
  if (x > y) x = y;
}
void Main() {
  fill(cnt, cnt + 26, 0);
  scanf("%d", &n);
  for (int i = 0, iE = n; i <= iE; i++)
    for (int j = 0, jE = n; j <= jE; j++) dp[i][j] = inf;
  scanf("%s%s", s + 1, t + 1);
  for (int i = 1, iE = n; i <= iE; i++) cnt[s[i] - 'a']++, cnt[t[i] - 'a']--;
  for (int i = 0, iE = 25; i <= iE; i++)
    if (cnt[i]) return puts("-1"), void();
  for (int i = 1, iE = n; i <= iE; i++)
    for (int j = 0, jE = 25; j <= jE; j++)
      qzs[i][j] = qzs[i - 1][j] + (s[i] == 'a' + j),
      qzt[i][j] = qzt[i - 1][j] + (t[i] == 'a' + j);
  for (int i = 0, iE = n; i <= iE; i++) dp[0][i] = 0;
  for (int i = 1, iE = n; i <= iE; i++)
    for (int j = i, jE = n; j <= jE; j++) {
      Min(dp[i][j], dp[i - 1][j] + 1);
      if (s[i] == t[j]) Min(dp[i][j], dp[i - 1][j - 1]);
      if (qzs[i][t[j] - 'a'] < qzt[j][t[j] - 'a']) Min(dp[i][j], dp[i][j - 1]);
    }
  printf("%d\n", dp[n][n]);
}
int main() {
  scanf("%d", &T);
  while (T--) Main();
  return 0;
}
