#include <bits/stdc++.h>
using namespace std;
#define pii pair<int, int>
const int N = 200200, M = 20;
int T, n, m;
char a[N];
bool res;
vector<pii> q;
vector<int> to[N];
int dfn[N], low[N], nw, st[N], top, ct;
int id[N];
bool cut[N];
int fa[N][M], dep[N];
int vis[N], cls;
void dfs(int u, int dps) {
	vis[u] = cls, dep[u] = dps;
	for (int v : to[u]) {
		if (vis[v]) continue;
		fa[v][0] = u;
		for (int j = 1; j < M; ++j) fa[v][j] = fa[fa[v][j - 1]][j - 1];
		dfs(v, dps + 1);
	}
	return;
}
int lca(int u, int v) {
	if (dep[u] < dep[v]) swap(u, v);
	for (int i = M - 1; i >= 0; --i) if (dep[fa[u][i]] >= dep[v]) u = fa[u][i];
	if (u == v) return u;
	for (int i = M - 1; i >= 0; --i) if (fa[u][i] != fa[v][i]) u = fa[u][i], v = fa[v][i];
	return fa[u][0];
}
void tarjan(int u, int rt) {
	dfn[u] = low[u] = ++nw, st[++top] = u;
	int s = 0;
	for (int v : to[u]) {
		if (!dfn[v]) {
			tarjan(v, rt), low[u] = min(low[u], low[v]), ++s;
			if (low[v] == dfn[u]) {
				if (s > 1 || u != rt) cut[u] = 1;
				++ct;
				while (top && st[top] != v) {
					id[st[top]] = ct;
					--top;
				}
				id[v] = ct, --top;
			}
		}
		else low[u] = min(low[u], dfn[v]);
	}
	return;
}
int main() {
	scanf("%d", &T);
	while (T--) {
		scanf("%d%d%s", &n, &m, a + 1);
		for (int i = 1; i <= n; ++i) vis[i] = dfn[i] = low[i] = cut[i] = 0, to[i].clear();
		res = cls = ct = top = nw = 0, q.clear();
		for (int i = 1, u, v; i <= m; ++i) {
			scanf("%d%d", &u, &v);
			if (a[u] != a[v]) to[u].push_back(v), to[v].push_back(u);
			else q.emplace_back(u, v);
		}
		cls = 1, dfs(1, 1), tarjan(1, 1);
		for (pii cc : q) {
			int u = cc.first, v = cc.second;
			if (!vis[u] || !vis[v]) continue;
			int w = lca(u, v), ww = fa[w][0];
			if (w == u || w == v || id[ww] && (id[ww] == id[u] || id[ww] == id[v])) {
				res = 1;
				break;
			}
		}
		puts(res ? "yes" : "no");
	}
	return 0;
}