#include<bits/stdc++.h>
using namespace std;
const int N=4e5+999,L=19;
int n,m,cnt;
string str;
vector<int> to[N];
struct edge{
	int v,nxt;
}edg[N*2];
int cntedge,hd[N];
void add(int u,int v){
	edg[++cntedge]=(edge){v,hd[u]};
	hd[u]=cntedge;
}
vector< pair<int,int> > e;
stack<int> sta;
int dfn[N],low[N],st[N],ed[N],timer,f[N][L];
void dfs(int u){
	int vv;
	dfn[u]=low[u]=++timer;
	sta.push(u);
	for(int v:to[u]){
		if(dfn[v]) low[u]=min(low[u],dfn[v]);
		else{
			dfs(v); low[u]=min(low[u],low[v]);
			if(low[v]>=dfn[u]){
				cnt++;
				do{
					vv=sta.top(); sta.pop();
					add(vv,cnt); add(cnt,vv);
				}while(vv!=v);
				add(u,cnt); add(cnt,u);
			}
		}
	}
	return;
}
void dfs(int u,int fa){
	st[u]=++timer;
	f[u][0]=fa;
	for(int i=1;i<L;i++)
		f[u][i]=f[f[u][i-1]][i-1];
	int v;
	for(int i=hd[u];i;i=edg[i].nxt){
		v=edg[i].v;
		if(v==fa) continue;
		dfs(v,u);
	}
	ed[u]=++timer;
	return;
}
bool judge(int u,int v){
	if(!u) return true;
	return st[u]<=st[v]&&ed[v]<=ed[u];
}
int lca(int u,int v){
	if(judge(u,v)) return u;
	if(judge(v,u)) return v;
	for(int i=L-1;i>=0;i--)
		if(!judge(f[u][i],v))
			u=f[u][i];
	return f[u][0];
}
void clr(){
	e.clear();
	for(int i=1;i<=n;i++){
		dfn[i]=low[i]=0;
		to[i].clear();
	}
	for(int i=1;i<=cnt;i++)
		st[i]=ed[i]=hd[i]=0;
	cntedge=timer=0;
	while(!sta.empty()) sta.pop();
}
int cntt;
void solve(){
	cntt++;
	cin>>n>>m>>str;
	if(cntt==9990) cout<<n<<" "<<m<<endl<<str<<endl;
	str=" "+str;
	int u,v,lc;
	for(int i=1;i<=m;i++){
		cin>>u>>v; u++; v++;
		if(cntt==9990) cout<<u<<" "<<v<<endl; 
		if(str[u]==str[v]) e.push_back(make_pair(u,v));
		else to[u].push_back(v),to[v].push_back(u);
	}
	cnt=n;
	dfs(1);
	timer=0;
	dfs(1,0);
	bool ans=0;
	for(pair<int,int> now:e){
		u=now.first; v=now.second;
		if(!dfn[u]||!dfn[v]) continue;
		lc=lca(u,v);
		if(lc==u||lc==v||lc>n) ans=1;
	}
	clr();
	if(cntt>2) return;
	if(ans) cout<<"yes"<<'\n';
	else cout<<"no"<<'\n';
	return;
}
int main(){
	std::ios::sync_with_stdio(false);
	cin.tie(0);
	int T; cin>>T;
	while(T--) solve();
	return 0;
}