#include <bits/stdc++.h>
#define rep1(i, l, r) for (int i = l; i <= int(r); ++i)
#define rep2(i, l, r) for (int i = l; i >= int(r); --i)
#define rer(i, l, r, a) rep1(i, l, r) read(a[i])
#define ptc putchar
#define il inline
#define eb emplace_back
#define ef emplace_front
#define mp make_pair
#define fst first
#define snd second
#define sqr(x) ((x) * (x))
#define ls(x) x << 1
#define rs(x) x << 1 | 1
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
// typedef __int128 bll;
// typedef unsigned __int128 ubll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
const int MAXN = 4e5 + 10, LOGN = log2(MAXN) + 1, inf = ~0U >> 2, INF = ~0U >> 1;
const int dx[] = {0, 0, 1, -1}, dy[] = {1, -1, 0, 0};
namespace stupid_lrc {
	template <typename T> il bool read(T &x) {
		x = 0; bool f = false; char ch;
 		while (!isdigit(ch = getchar())) {
			f ^= !(ch ^ '-');
			if (ch == EOF) return false;
		}
		while (isdigit(ch)) x = (x << 1) + (x << 3) + (ch & 15), ch = getchar();
		if (f) x = ~x + 1; return true;
	}
	il int read() {int x; read(x); return x;}

	template <typename T> il bool read(pair <T, T> &x) {return read(x.fst) && read(x.snd);}

	template <typename T> il void gmin(T &x, T y) {x = x < y ? x : y;}

 	template <typename T> il void gmax(T &x, T y) {x = x > y ? x : y;}

	template <typename T, typename ...L>
	il bool read(T &x, L &...y) {return read(x) && read(y...);}

	template <typename T> il T lowbit(const T &x) {return x & -x;}
}
using namespace stupid_lrc;
int n, m, dfn[MAXN], low[MAXN], stp, st[MAXN], idx, tot, f[MAXN][20], lg[MAXN], dep[MAXN];
char s[MAXN]; vector <int> lnk[MAXN], lnk2[MAXN];

il void add(const int &x, const int &y) {
	lnk[x].eb(y); lnk[y].eb(x);
}

il void add2(const int &x, const int &y) {
	lnk2[x].eb(y); lnk2[y].eb(x);
}

il void dfs(int x) {
	dfn[x] = low[x] = ++stp; st[++idx] = x;
	for (auto v : lnk[x]) {
		if (!dfn[v]) {
			dfs(v); gmin(low[x], low[v]);
			if (dfn[x] == low[v]) {
				++tot;
				for (int x = -1; x ^ v; ) {
					x = st[idx--];
					add2(tot, x);
				} add2(tot, x);
			}
		} else gmin(low[x], dfn[v]);
	}
}

il void dfs2(int x, int p) {
	f[x][0] = p; dep[x] = dep[p] + 1;
	for (auto v : lnk2[x]) if (v ^ p) dfs2(v, x);
}

il int lca(int u, int v) {
	if (dep[u] < dep[v]) swap(u, v);
	rep2(i, lg[n] + 1, 0) if (dep[u] - dep[v] >= 1 << i) u = f[u][i];
	if (u == v) return u;
	rep2(i, lg[n] + 1, 0) if (f[u][i] ^ f[v][i]) u = f[u][i], v = f[v][i];
	return f[u][0];
}

il void solve() {
	read(n, m); scanf("%s", s + 1);
	vector <pii> smc;
	rep1(i, 1, m) {
		int u, v; read(u, v); ++u; ++v;
		if (s[u] != s[v]) add(u, v);
		else smc.eb(u, v);
	} tot = n; idx = stp = 0; dfs(1); dfs2(1, 0);
	rep1(j, 1, lg[n] + 1) rep1(i, 1, tot) f[i][j] = f[f[i][j - 1]][j - 1];
	f[1][0] = 1;
	bool flg = 0;
	for (auto t : smc) {
		int u, v; tie(u, v) = t;
		u = f[u][0], v = f[v][0];
		int q = lca(u, v);
		if (u && v && (q == u || q == v)) {
			flg = 1;
			break;
		}
	} puts(flg ? "yes" : "no");
	rep1(i, 1, n << 1) lnk[i].clear(), lnk2[i].clear(), dfn[i] = f[i][0] = 0;
}

int main() {
	rep1(i, 2, 4e5) lg[i] = lg[i >> 1] + 1;
	for (int T = read(); T--; ) solve();
	return 0;
}