#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());}
}