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

const int N = 2e5 + 100;
int n, m,sum=0;
char s[N];
vector <int> G[N], Gv[N];
bool in[N], ans, inn[N], vis[N];
int deg[N], mindeg[N], fa[N][21],v;

void dfs0(int now, int father) {
    inn[now] = 1; deg[now] = deg[father] + 1; fa[now][0] = father; vis[now] = 1;
    for (int i = 0; i < G[now].size(); i++) {
        int x = G[now][i]; if (x == father || inn[x]) continue;
        dfs0(x, now);
    }
}

int LCA(int x, int y) {
    if (deg[x] < deg[y]) swap(x, y);
    for (int i = 20; i >= 0; i--)
        if (deg[fa[x][i]] >= deg[y]) x = fa[x][i];
    if (x == y) return x;
    for (int i = 20; i >= 0; i--)
        if (fa[x][i] != fa[y][i]) x = fa[x][i], y = fa[y][i];
    return fa[x][0];
}

void dfs(int now, int father) {
    inn[now] = 1;
    for (int i = 0; i < G[now].size(); i++) {
        int x = G[now][i]; if (x == father || inn[x]) continue;
        dfs(x, now);
    }
    mindeg[now] = deg[now];
    for (int i = 0; i < G[now].size(); i++) {
        if (G[now][i]==father)continue;
        int x = G[now][i];
        if(deg[x]>deg[now])mindeg[now] = min(mindeg[now], mindeg[x]);
        else mindeg[now]=min(mindeg[now],deg[x]);
    }
}

void dfs2(int now, int father) {
    inn[now] = 1; in[now] = 1; 
    for (int i = 0; i < G[now].size(); i++) {
        int x = G[now][i]; if (x == father || inn[x]) continue;
        dfs2(x, now);
    }
    for (int i = 0; i < Gv[now].size(); i++) {
        int x = Gv[now][i]; if (!vis[x]) continue;
        if (in[x]) {
            ans = 1;
            // printf("%d %d\n", now, x);
            // printf("qwq\n");
        }
        else if (deg[LCA(now, x)] > min(mindeg[now], mindeg[x])) {
            ans = 1;
            // printf("%d %d\n", now, x);
            // printf("awa\n");
        }
    }
    in[now] = 0;
}

void slove() {
    sum++;
    scanf("%d %d", &n, &m);
    if(v==4627&&sum==4516)cout<<n<<" "<<m<<endl;
    scanf("%s", s); ans = 0;
     if(v==4627&&sum==4516)cout<<s<<endl;
    for (int i = 1; i <= m; i++) {
        int x, y; scanf("%d %d", &x, &y);
        if(v==4627&&sum==4516)cout<<x<<" "<<y<<endl;
        if (s[x] == s[y]) Gv[x].push_back(y), Gv[y].push_back(x);
            else G[x].push_back(y), G[y].push_back(x);
    }

    dfs0(0, 0);
    for (int i = 0; i < n; i++) inn[i] = 0;
    for (int j = 1; j <= 20; j++)
        for (int i = 0; i < n; i++) fa[i][j] = fa[fa[i][j - 1]][j - 1];
    for (int i = 0; i < n; i++) mindeg[i] = n + 1;
    dfs(0, 0);
    for (int i = 0; i < n; i++) inn[i] = 0;
    dfs2(0, 0);
    if(v!=4627){
        if (ans) printf("yes\n");
        else printf("no\n");
    }
    

    for (int i = 0; i < n; i++) G[i].clear(), Gv[i].clear(), inn[i] = 0, in[i] = 0, deg[i] = 0, vis[i] = 0;
    for (int i = 0; i < n; i++)
        for (int j = 0; j <= 20; j++) fa[i][j] = 0;
}

int main() {
    int t; scanf("%d", &t);
    v=t;
    while (t--) slove();
    return 0;
}