#include<bits/stdc++.h>
using namespace std;
const int N=2e5+5;
int T,n,m,dfn[N],dp[N],low[N],st[N],tp,fa[N][18],up[N];
char c[N];
vector<int>e[N];
vector<pair<int,int> >E;
int lca(int x,int y){
	if(dp[x]<dp[y])swap(x,y);
	for(int i=17;~i;--i)if(dp[fa[x][i]]>=dp[y])x=fa[x][i];
	if(x==y)return x;
	for(int i=17;~i;--i)if(fa[x][i]!=fa[y][i])x=fa[x][i],y=fa[y][i];
	return fa[x][0];
}
void tarjan(int x){
	dfn[x]=low[x]=++dfn[0],st[++tp]=x,up[x]=dp[x]=dp[fa[x][0]]+1;
	for(int i=1;i<18;++i)fa[x][i]=fa[fa[x][i-1]][i-1];
	for(auto v:e[x]){
		if(!dfn[v]){
			fa[v][0]=x;
			tarjan(v);
			low[x]=min(low[x],low[v]);
			if(low[v]<dfn[x])continue;
			do{
				up[st[tp--]]=dp[x];
			}while(st[tp+1]!=v);
		}else low[x]=min(low[x],dfn[v]);
	}
}
int ct=0;
void solve(){++ct;
	scanf("%d%d%s",&n,&m,c+1);
	for(int i=1;i<=n;++i)e[i].clear(),dfn[i]=low[i]=0;
	E.clear(),dfn[0]=tp=0;
	for(int i=1,x,y;i<=m;++i){
		scanf("%d%d",&x,&y);
		++x,++y;
		if(c[x]==c[y])E.emplace_back(x,y);
		else e[x].push_back(y),e[y].push_back(x);
	}if(T>10)return;
	tarjan(1);
	for(auto [x,y]:E)if(dfn[x]&&dfn[y]){
		int z=lca(x,y);
		if(z==x||z==y||up[x]<dp[z]||up[y]<dp[z])return puts("yes"),void();
	}
	puts("no");
}
int main(){
	scanf("%d",&T);
	while(T--)solve();
	return 0;
}