#include <bits/stdc++.h>
using namespace std;
const int N = 4e5 + 10;
struct Edge {
  int u, v;
} E[N];
struct Node {
  int nxt, v;
} G[N * 2];
int n, m, head[N], cnt = 1, seq[N], rnk[N], siz[N], fa[N];
int dfn[N], low[N], tim, in[N], sta[N], top, bcc, c[N];
char s[N];
vector<int> T[N], q[N];
void AddE(int u, int v) {
  G[++cnt] = {head[u], v}, head[u] = cnt;
  G[++cnt] = {head[v], u}, head[v] = cnt;
}
void Tarjan(int u, int fat) {
  dfn[u] = low[u] = ++tim;
  in[u] = 1, sta[++top] = u;
  for(int i = head[u]; i; i = G[i].nxt) if(i != fat) {
    int v = G[i].v;
    if(!dfn[v]) {
      Tarjan(v, i ^ 1), low[u] = min(low[u], low[v]);
      if(low[v] >= dfn[u]) {
        int x; T[u].push_back(++bcc);
        do x = sta[top--], in[x] = 0, T[bcc].push_back(x);
        while(x != v);
      }
    }
    else if(in[v]) low[u] = min(low[u], dfn[v]);
  }
}
void Dfs(int u) {
  seq[rnk[u] = ++rnk[0]] = u, siz[u] = 1;
  for(int v : T[u]) fa[v] = u, Dfs(v), siz[u] += siz[v];
}
void Add(int pos, int k) {
  while(pos <= rnk[0])
    c[pos] += k, pos += pos & -pos;
}
int Sum(int pos) {
  int ans = 0;
  while(pos)
    ans += c[pos], pos -= pos & -pos;
  return ans;
}
void Mdf(int u, int k) {
  Add(rnk[u], k);
  Add(rnk[u] + siz[u], -k);
}
int Qry(int u) {
  return Sum(rnk[u]);
}
void Solve() {
  scanf("%d%d%s", &n, &m, &s[1]);
  for(int i = 1; i <= m; ++i) {
    int u, v; scanf("%d%d", &u, &v); 
    ++u, ++v, E[i] = {u, v};
    if(s[u] != s[v]) AddE(u, v);
  }
  bcc = n, Tarjan(1, 0);
  Dfs(1);
  bool flag = 0;
  for(int i = 1; i <= m; ++i) {
    int u = E[i].u, v = E[i].v;
    if(s[u] == s[v]) {
      if(u == 1 || v == 1) flag = 1;
      q[u].push_back(v), q[v].push_back(u);
    }
  }
  for(int u = 1; u <= n; ++u) if(dfn[u]) {
    for(int x : T[u]) 
      Mdf(x, 1);
    if(fa[u]) Mdf(fa[u], 1);
    for(int v : q[u])
      if(Qry(v))
        flag = 1;
    for(int x : T[u]) 
      Mdf(x, -1);
    if(fa[u]) Mdf(fa[u], -1);

  }
  printf(flag ? "yes\n" : "no\n");
  for(int i = 1; i <= m; ++i) E[i] = {0, 0};
  for(int i = 2; i <= cnt; ++i) G[i] = {0, 0};
  for(int i = 1; i <= n; ++i)
    head[i] = dfn[i] = low[i] = in[i] = 0,
    q[i].resize(0);
  for(int i = 1; i <= rnk[0]; ++i)
    seq[i] = 0;
  for(int i = 1; i <= bcc; ++i)
    siz[i] = fa[i] = 0,
    T[i].resize(0);
  cnt = 1, rnk[0] = top = tim = 0;
}
int main() {
  //freopen("data.in", "r", stdin);
  //freopen("code.out", "w", stdout);
  int t; scanf("%d", &t);
  while(t--) Solve();
  return 0;
}