#include <bits/stdc++.h>

using LL = long long ;

#define ALL(v) (v).begin(),(v).end()

#define showtime fprintf(stderr,"time = %.15f\n",clock() / (double)CLOCKS_PER_SEC)

char str[100][11];

int n,m;

int weight[100];

const int N = 10 * 100 + 5;

int go[N][26],val[N],fail[N],tot;

int get_node() {

    memset(go[tot],-1,sizeof(go[tot]));

    val[tot] = 0;

    return tot ++;

}

int dp[50 + 1][N],pre[50 + 1][N],pc[50 + 1][N];

std::vector<int> order[50 + 1];

void insert(char *s,int w) {

    int u = 0;

    for ( ; *s; ++ s) {

        int c = *s - 'a';

        if (go[u][c] == -1)

            go[u][c] = get_node();

        u = go[u][c];

    }

    val[u] += w;

}

std::string work() {

    tot = 0;

    get_node();

    for (int i = 0; i < m; ++ i) {

        insert(str[i],weight[i]);

    }

    std::vector<int> vec{0};

    fail[0] = -1;

    for (int I = 0; I < (int)vec.size(); ++ I) {

        int u = vec[I];

        for (int c = 0; c < 26; ++ c) {

            if (go[u][c] == -1) continue;

            int v = go[u][c];

            int f = fail[u];

            while (f != -1 && go[f][c] == -1) f = fail[f];

            fail[v] = f == -1 ? 0 : go[f][c];

            vec.push_back(v);

        }

    }

    for (int I = (int)vec.size() - 1; I >= 0; -- I) {

        int u = vec[I];

        for (int c = 0; c < 26; ++ c) {

            int f = u;

            while (f != -1 && go[f][c] == -1) f = fail[f];

            go[u][c] = f == -1 ? -1 : go[f][c];

        }

        for (int f = fail[u]; f != -1; f = fail[f]) {

            val[u] += val[f];

        }

    }

    memset(dp,-1,sizeof(dp));

    memset(pre,-1,sizeof(pre));

    dp[0][0] = 0;

    for (int i = 0; i <= n; ++ i) {

        order[i].clear();

    }

    order[0].push_back(0);

    for (int i = 0; i < n; ++ i) {

        for (int u : order[i]) {

            for (int c = 0; c < 26; ++ c) {

                if (go[u][c] == -1) continue;

                int v = go[u][c];

                dp[i + 1][v] = std::max(dp[i + 1][v],dp[i][u] + val[v]);

            }

        }

        for (int u : order[i]) {

            for (int c = 0; c < 26; ++ c) {

                if (go[u][c] == -1) continue;

                int v = go[u][c];

                if (dp[i + 1][v] == dp[i][u] + val[v] && pre[i + 1][v] == -1) {

                    pre[i + 1][v] = u;

                    pc[i + 1][v] = c;

                    order[i + 1].push_back(v);

                }

            }

        }

    }

    int ai = 0,au = 0;

    for (int i = 0; i <= n; ++ i) {

        for (int u : order[i]) {

            if (dp[i][u] > dp[ai][au]) {

                ai = i;

                au = u;

            }

        }

    }

    std::string ret;

    while (ai) {

        ret.push_back(pc[ai][au] + 'a');

        au = pre[ai][au];

        -- ai;

    }

    std::reverse(ALL(ret));

    return ret;

}

int main() {

    int cas;

    scanf("%d",&cas);

    while (cas--) {

        scanf("%d%d",&n,&m);

        for (int i = 0; i < m; ++ i) {

            scanf("%s",str[i]);

        }

        for (int i = 0; i < m; ++ i) {

            scanf("%d",weight + i);

        }

        printf("%s\n",work().c_str());

    }

}