#include<iostream>
#include<utility>
#include<stack>
#include<vector>
#define N 200005
#define K 18
using namespace std;
typedef pair<int,int>pii; 
vector<int>g[N];
pii e[N];
char c[N];
int dfn[N],low[N],fa[N][K],to[N],dep[N];
stack<int>s;
void dfs(int u,int f)
{
	dfn[u]=low[u]=++dfn[0],fa[u][0]=f,dep[u]=dep[f]+1;s.push(u);
	for(int k=1;k<K;++k)fa[u][k]=fa[fa[u][k-1]][k-1];
	for(int v:g[u])if(v!=f)
	{
		if(dfn[v]){low[u]=min(low[u],dfn[v]);continue;}
		dfs(v,u);low[u]=min(low[u],low[v]);
		if(low[v]>=dfn[u])
			for(int t=-1;t!=v;)
			{
				t=s.top();s.pop();
				to[t]=u;
			}
	}
}
int lca(int u,int v)
{
	if(dep[u]<dep[v])swap(u,v);
	for(int k=K-1;~k;--k)if(dep[fa[u][k]]>=dep[v])u=fa[u][k];
	if(u==v)return u;
	for(int k=K-1;~k;--k)if(fa[u][k]!=fa[v][k])u=fa[u][k],v=fa[v][k];
	return fa[u][0];
}
void solve()
{
	int n,m;cin>>n>>m>>c+1;
	int cnt=0;dfn[0]=0;
	for(int i=1;i<=n;++i)g[i].clear(),dfn[i]=to[i]=0;
	for(int i=1;i<=m;++i)
	{
		int u,v;cin>>u>>v;++u,++v;
		if(c[u]!=c[v])g[u].push_back(v),g[v].push_back(u);
		else e[++cnt]={u,v};
	}
	while(!s.empty())s.pop();
	dfs(1,0);
	for(int i=1;i<=cnt;++i)
	{
		int u=e[i].first,v=e[i].second;
		if(!dfn[u]||!dfn[v])continue;
		int w=lca(u,v);
		if(to[w]==to[u]||to[w]==to[v]){cout<<"yes\n";return;}
	}
	cout<<"no\n";return;
}
int main()
{
	ios::sync_with_stdio(0),cin.tie(nullptr),cout.tie(nullptr);
	int t;cin>>t;while(t--)solve();
	return 0;
}