#include<bits/stdc++.h>
using namespace std;
const int N = 2e5 + 5, M = 2e5 + 5, B = 17;
int T, n, m, fir[N], nxt[M << 1], son[M << 1], tot, to[N], idx, x, y, z;
int fa[N][18], dfn[N], low[N], stk[N], t, dep[N];
char s[N];
struct node{
    int x, y;
};
vector<node> vec;
inline void add(int x, int y){
    nxt[++tot] = fir[x];
    fir[x] = tot;
    son[tot] = y;
}
inline void init(){
    vec.clear();
    for(int i = 1; i <= n; i++){
        fir[i] = to[i] = 0;
        dfn[i] = 0;
    }
    for(int i = 1; i <= n; i++) stk[i] = 0;
    tot = idx = t = 0;
}
inline void tarjan(int x){
    dfn[x] = low[x] = ++idx;
    stk[++t] = x;
    dep[x] = dep[fa[x][0]] + 1;
    for(int i = 1; i <= B; i++) fa[x][i] = fa[fa[x][i - 1]][i - 1];
    for(int i = fir[x]; i ; i = nxt[i]){
        if(dfn[son[i]]){
            low[x] = min(low[x], dfn[son[i]]);
            continue ;
        }
        fa[son[i]][0] = x;
        tarjan(son[i]);
        low[x] = min(low[x], low[son[i]]);
        if(low[son[i]] >= dfn[x]){
            while(stk[t + 1] ^ son[i]){
                to[stk[t]] = x;
                t--;
            }
        }
    }
}
inline int lca(int x, int y){
    if(dep[x] > dep[y]) swap(x, y);
    for(int i = B; ~i; i--){
        if(dep[fa[y][i]] >= dep[x]){
            y = fa[y][i];
        }
    }
    if(x == y) return x;
    for(int i = B; ~i; i--){
        if(fa[x][i] ^ fa[y][i]){
            x = fa[x][i], y = fa[y][i];
        }
    }
    return fa[x][0];
}
inline void solve(){
    init();
    scanf("%d%d%s", &n, &m, s + 1);
    for(int i = 1; i <= m; i++){
        scanf("%d%d", &x, &y);x++, y++;
        if(s[x] == s[y]){
            vec.push_back((node){x, y});
        }
        else{
            add(x, y), add(y, x);
        }
    }
    dep[1] = 1;
    tarjan(1);
    for(node e : vec){
        x = e.x, y = e.y;
        if(!dfn[x] || !dfn[y]) continue ;
        z = lca(x, y);
        // cerr << x << ' ' << y << ' ' << z << ' ' << to[x] << ' ' << to[y] << ' ' << to[z] << endl;
        if(z == x || z == y || to[z] == to[x] || to[z] == to[y]){
            puts("yes");
            return ;
        }
    }
    puts("no");
}
int main(){
    scanf("%d", &T);
    while(T--){
        solve();
    }
    return 0;
}