#include <iostream>

#include <atcoder/modint>
#include <atcoder/convolution>

using mint = atcoder::modint998244353;

namespace atcoder {
    std::istream& operator>>(std::istream& in, mint& a) {
        long long e; in >> e; a = e;
        return in;
    }

    std::ostream& operator<<(std::ostream& out, const mint& a) {
        out << a.val();
        return out;
    }
} // namespace atcoder

void solve() {
    int n, m;
    std::cin >> n >> m;

    std::string s, t;
    std::cin >> s >> t;

    std::reverse(s.begin(), s.end());

    std::vector<mint> f0(n), f1(n), f2(n);
    std::vector<mint> g0(m), g1(m), g2(m);
    for (int i = 0; i < n; ++i) {
        f0[i] = (s[i] == '?') ? 0 : 1;
        f1[i] = f0[i] * s[i];
        f2[i] = f1[i] * s[i];
    }
    for (int j = 0; j < m; ++j) {
        g0[j] = 1;
        g1[j] = g0[j] * t[j];
        g2[j] = g1[j] * t[j];
    }
    std::vector<mint> h(n + m - 1);
    std::vector<mint> f2g0 = atcoder::convolution(f2, g0);
    std::vector<mint> f1g1 = atcoder::convolution(f1, g1);
    std::vector<mint> f0g2 = atcoder::convolution(f0, g2);
    for (int i = 0; i < n + m - 1; ++i) {
        h[i] += f2g0[i] - 2 * f1g1[i] + f0g2[i];
    }
    for (int i = m - 1; i < n; ++i) {
        if (h[i] == 0) {
            for (int j = 0; j < m; ++j) {
                s[i - j] = t[j];
            }
            std::replace(s.begin(), s.end(), '?', 'a');
            std::reverse(s.begin(), s.end());
            std::cout << s << '\n';
            return;
        }
    }
    std::cout << -1 << '\n';
}

int main() {
    std::ios::sync_with_stdio(false);
    std::cin.tie(nullptr);

    int t;
    std::cin >> t;
    while (t-- > 0) {
        solve();
    }
}