/*
无限走的充要条件：可以走回一个已经走过的点
*/
#include <bits/stdc++.h>
using namespace std;
typedef pair<int, int> pii;
int n, m;
char s[200200];
vector<int> q[200200], e[200200];
bool vis[200200], fu[200200];
int fa[200200];
int dfn[200200], low[200200], cntdfn;
bool flag;
map<pii, int> lca;
stack<int> st;
int col[200200], cc;
int getfa(int x) { return fa[x] == x ? x : (fa[x] = getfa(fa[x])); }
void merge(int x, int y) { fa[getfa(x)] = getfa(y); }
void dfs(int x, int f = 0) {
    low[x] = dfn[x] = ++cntdfn;
    vis[x] = 1;
    fu[x] = 1;
    st.push(x);
    for (int y : e[x]) {
        if (!vis[y]) {
            dfs(y, x);
            low[x] = min(low[x], low[y]);
            if (low[y] >= dfn[x]) {
                cc++;
                while (st.top() != y) {
                    col[st.top()] = cc;
                    st.pop();
                }
                col[st.top()] = cc;
                st.pop();
            }
        } else if (fu[y]) low[x] = min(low[x], dfn[y]);
    }
    for (int y : q[x]) if (vis[y]) {
        int l = getfa(y);
        lca[make_pair(x, y)] = lca[make_pair(y, x)] = l;
        if (fu[y]) flag = 1;
    }
    fu[x] = 0;
    merge(x, f);
}
void _main() {
    scanf("%d%d%s", &n, &m, s + 1);
    flag = cntdfn = 0;
    cc = 0;
    for (int i = 1; i <= n; i++) fa[i] = i, q[i].clear(), e[i].clear(), vis[i] = 0, col[i] = 0;
    for (int i = 1; i <= m; i++) {
        int u, v;
        scanf("%d%d", &u, &v);
        u++, v++;
        if (s[u] != s[v]) e[u].push_back(v), e[v].push_back(u);
        else q[u].push_back(v), q[v].push_back(u);
    }
    dfs(1);
    for (int i = 1; i <= n; i++) for (int j : q[i]) {
        int l = lca[make_pair(i, j)];
        if (getfa(i) != getfa(j)) continue;
        if (col[l] == col[i] || col[l] == col[j]) flag = 1;
    }
    if (flag) printf("yes\n");
    else printf("no\n");
}
int main() {
    // freopen("travel.in", "r", stdin);
    // freopen("travel.out", "w", stdout);
    int T;
    scanf("%d", &T);
    while (T--) _main();
    return 0;
}