#include <bits/stdc++.h>
const int N = 2e5 + 10;
std::vector<int> G[N], T[N];
int idf[N * 2], odf[N * 2], dfn[N], low[N];
int sta[N], top;
char str[N];
int scc[N * 2], cov[N], fa[N * 2];
int idx, tot, n;
struct Edge { int u, v; };
void tarjan (int u) {
    dfn[u] = low[u] = ++idx;
    sta[++top] = u;
    for (int v : G[u]) {
        if (!dfn[v]) {
            tarjan(v);
            low[u] = std::min(low[u], low[v]);
            if (low[v] >= dfn[u]) {
                ++tot;
                scc[tot] = tot;
                T[u].push_back(tot);
                auto ins = [&](int x) { 
                    ++cov[x], scc[x] = tot;
                    T[tot].push_back(x);
                };
                ins(u);
                do { ins(sta[top]); } while (sta[top--] != v);
            }
        }
        else low[u] = std::min(low[u], dfn[v]);
    }
}
void Dfs (int u) {
    idf[u] = ++idx;
    for (int v : T[u]) {
        if (v == fa[u]) continue;
        fa[v] = u;
        Dfs(v);
    }
    odf[u] = idx;
}
void solve () {
    for (int i = 1; i <= tot; ++i) idf[i] = odf[i] = 0;
    for (int i = 1; i <= n; ++i) dfn[i] = low[i] = cov[i] = 0;
    for (int i = 1; i <= tot; ++i) scc[i] = 0;
    for (int i = 1; i <= n; ++i) G[i].clear();
    for (int i = 1; i <= tot; ++i) T[i].clear();
    idx = top = 0;
    int m;
    std::cin >> n >> m;
    tot = n;
    std::vector<Edge> vec;
    std::cin >> (str + 1);
    for (int i = 1; i <= m; ++i) {
        int u, v;
        std::cin >> u >> v;
        ++u, ++v;
        if (str[u] == str[v]) vec.push_back({u, v});
        else {
            G[u].push_back(v);
            G[v].push_back(u);
        }
    }
    tarjan(1);
    // printf("scc: %d\n", scc[1]);
    idx = 0, fa[1] = 0;
    Dfs(1);
    // printf("%d\n", (int)vec.size());
    for (Edge t : vec) {
        int u = t.u, v = t.v;
        // printf("%d %d\n", u, v);
        if (!idf[u] || !idf[v]) continue;
        int x = scc[u], y = scc[v];
        // printf("xy: %d %d\n", u, v);
        // printf("fxy: %d %d\n", fa[u], fa[v]);
        // printf("cxy: %d %d\n", cov[u], cov[v]);
        if (cov[u] > 1 && fa[u]) x = scc[fa[u]];
        if (cov[v] > 1 && fa[v]) y = scc[fa[v]];
        if (idf[x] > idf[y]) std::swap(x, y);
        // printf("xy: %d %d\n", x, y);
        if (odf[x] >= idf[y])
            { puts("yes"); return; }
    }
    puts("no");
}
int main () {
    // freopen("travel.in", "r", stdin);
    // freopen("travel.out", "w", stdout);
    std::cin.tie(0)->sync_with_stdio(0);
    int T;
    std::cin >> T;
    while (T--) solve();
}