#include<bits/stdc++.h>
using namespace std;

const int mod=998244353;

int calc(char c){
    return c-'a';
}

inline int fpow(int x, int t = mod - 2) {
    int res = 1;
    for (; t; t >>= 1, x = 1ll * x * x % mod)
        if (t & 1) res = 1ll * res * x % mod;
    return res;
}

struct ACAM{
    struct node{
        int son[26],trans[26];int fail=0;double val=0;double ans=-1e9;int trueans=0;int len=0;
    };
    node trie[4000+10];
    int cnt=0;int rt=0;
    int res=0;
    void initial(){
        rt=0;cnt=0;
        res=0;
        for(int i=0;i<=4000;i++){
            memset(trie[i].son,0,sizeof(trie[i].son));
            memset(trie[i].trans,0,sizeof(trie[i].trans));
            trie[i].fail=0;trie[i].val=0;
            trie[i].ans=-1e9;trie[i].trueans=-1e9;
            trie[i].len=0;
        }
    }

    void insert(string str,int val){
        int p=rt;
        for(auto s:str){
            if(!trie[p].son[calc(s)]){
                trie[p].son[calc(s)]=++cnt;
            }
            p=trie[p].son[calc(s)];
        }
        trie[p].val=val;
    }
    void build(){
        queue<int> q;q.push(rt);
        while(!q.empty()){
            int te=q.front();
            node cur=trie[te];
            q.pop();
            for(int i=0;i<26;i++){
                if(cur.son[i]){
                    node temp=trie[cur.son[i]];
                    temp.fail=cur.fail;
                    while(temp.fail&&!trie[temp.fail].son[i]){
                        temp.fail=trie[temp.fail].fail;
                    }
                    if(te&&trie[temp.fail].son[i]){
                        trie[cur.son[i]].fail=trie[temp.fail].son[i];
                    }
                    trie[cur.son[i]].val+=trie[trie[cur.son[i]].fail].val;
                    trie[te].trans[i]=trie[te].son[i];
                    q.push(cur.son[i]);
                }
                else{
                    trie[te].trans[i]=trie[trie[te].fail].trans[i];
                }
            }
        }
    }

    bool check(string str,double x){
        res=0;
        for(int i=0;i<=cnt;i++){trie[i].ans=-1e9;trie[i].trueans=0;trie[i].len=0;}
        trie[0].ans=0;trie[0].trueans=0;trie[0].len=0;
        for(auto s:str){
            for(int i=cnt;i>=0;i--){
                if(trie[i].ans>-1e9){
                    node* temp=&(trie[trie[i].trans[calc(s)]]);
                    if(trie[i].ans+temp->val-x>temp->ans){
                        temp->ans=trie[i].ans+temp->val-x;
                        temp->trueans=(1ll*(trie[i].trueans)+((int)temp->val))%mod;
                        temp->len=trie[i].len+1;
                    }
                }
            }   
        }
        for(int i=1;i<=cnt;i++){
            if(trie[i].ans>=0){res=i;return true;}
        }
        return false;
    }

    int cal(){
        return 1ll*trie[res].trueans*fpow(trie[res].len)%mod;
    }
    void print(){
        for(int i=0;i<=20;i++){
            printf("%d %d\n",trie[i].trueans,trie[i].len);
        }
    }
};

ACAM dir;
string arr[200000+10];

int main(){
    int t;scanf("%d",&t);
    while(t--){
        dir.initial();
        int n,m;scanf("%d%d",&n,&m);
        string s;cin>>s;
        for(int i=1;i<=m;i++){
            cin>>arr[i];
            int val;scanf("%d",&val);
            dir.insert(arr[i],val);
        }
        dir.build();
        double l=0.0,r=1e5+0.0, eps=1e-8;
        while(r-l>eps){
            double mid=(l+r)/2;
            if(dir.check(s,mid)){l=mid;}
            else{r=mid;}
        }
        dir.check(s,l);
        //dir.print();
        printf("%d\n",dir.cal());
    }
    
    
    return 0;
}