#include<iostream>
#include<cmath>
#include<cstring>
#include<algorithm>
#include<queue>
#include<cstdio>
using namespace std;
inline int max(int x,int y){return x>y?x:y;}
const int M=2e6+5;
int T,n,m;
bool a[M];

int cnt=0;
struct node{
	int l,r;
};node e[M];
struct N{
	int to,next;
};N p[M<<1];
int head[M];

inline void add(int a,int b)
{
	//cout<<a<<" "<<b<<"!\n";
	++cnt;
	p[cnt].next=head[a];
	head[a]=cnt;
	p[cnt].to=b;
}

int fa[M],son[M],siz[M],deep[M],vis[M];
inline void dfs1(int u,int f,int d)
{
	vis[u]=1,deep[u]=d,siz[u]=1,fa[u]=f;
	for(int i=head[u];i!=0;i=p[i].next)
	{
		int v=p[i].to;
		if(v==f||vis[v]) continue;
		dfs1(v,u,d+1);
		siz[u]+=siz[v];
		if(siz[v]>siz[son[u]]) son[u]=v;
	}
}

int top[M];
inline void dfs2(int u,int topp)
{
	vis[u]=1,top[u]=topp;
	if(!son[u]) return ;
	dfs2(son[u],topp);
	for(int i=head[u];i!=0;i=p[i].next)
	{
		int v=p[i].to;
		if(top[v]||vis[v]) continue;
		dfs2(v,v);
	}
}
int tot=0,num=0,k=0;
int sta[M],col[M],dfn[M],low[M],pre[M];
vector<int> t[M];
inline int pos(int x){return pre[x]?2*n+x:n+col[x];}
inline void tarjan(int u,int root)//板子 
{
	dfn[u]=low[u]=++num;
	sta[++k]=u;
	if(u==root&&head[u]==0)
	{
		++tot;
		t[++tot].push_back(u);
		if(!pre[u]) col[u]=tot;
		return ;
	}
	for(int i=head[u],to,sum=0;i!=0;i=p[i].next)
	{
		int v=p[i].to;
		if(!dfn[v])
		{
			tarjan(v,root);
			low[u]=min(low[u],low[v]);
			if(low[v]>=dfn[u])
			{
				++sum;
				if(u!=root||sum>1) pre[u]=1;
				++tot;
				while(to!=v)
				{
					to=sta[k--];
					t[tot].push_back(to);
					if(!pre[to]) col[to]=tot;
				}
				t[tot].push_back(u);
				if(!pre[u]) col[u]=tot;
						
			}
		}
		else low[u]=min(low[u],dfn[v]);
	}
}

inline int lca(int x,int y)
{
	while(top[x]!=top[y])
	{
		if(deep[top[x]]<deep[top[y]]) swap(x,y);
		x=fa[top[x]];
	}
	if(deep[x]>deep[y]) return y;
	return x;
}

inline void solve()
{
	cin>>n>>m;
	char opt;int flag=0;
	for(int i=1;i<=n;++i) cin>>opt,a[i]=(opt=='H');
	for(int i=1;i<=m;++i)
	{
		cin>>e[i].l>>e[i].r;
		++e[i].l,++e[i].r; 
		if(a[e[i].l]==a[e[i].r]) continue;
		add(e[i].l,e[i].r),add(e[i].r,e[i].l);
	}
	//exit(0);
	tarjan(1,1);
	//for(int i=1;i<=n;++i) cout<<pre[i]<<" "<<col[i]<<" "<<dfn[i]<<" "<<low[i]<<"\n";
	//exit(0); 
	for(int i=1;i<=tot;++i)
	{
		for(auto it:t[i]) if(pre[it]) add(pos(it),i+n),add(i+n,pos(it));
	}
	dfs1(pos(1),0,1);
	for(int i=1;i<=min(M-1,3*n+10);++i)	vis[i]=0;
	dfs2(pos(1),pos(1));
    for(int i=1,lca_x,u,v;i<=m;++i)
    {
    	if(a[e[i].l]==a[e[i].r])
    	{
    		if(!dfn[e[i].l]||!dfn[e[i].r])continue;
    		u=pos(e[i].l),v=pos(e[i].r);
    		if(pre[e[i].l]&&e[i].l!=1) u=fa[u];
    		if(pre[e[i].r]&&e[i].r!=1) v=fa[v];
    		lca_x=lca(u,v);
    		//cout<<lca_x<<"\n"; 
    		if(u==lca_x||v==lca_x) flag=1;
    	}
    	if(flag) break;
    }
    if(flag) cout<<"yes\n";
	else cout<<"no\n";
}

signed main()
{
	ios::sync_with_stdio(false);
	cin.tie(0);cout.tie(0);
	//freopen("travel.in","r",stdin);
	//freopen("travel.out","w",stdout); 
	cin>>T;
	while(T--)
	{
		tot=k=cnt=num=0;
		for(int i=1;i<=min(M-1,3*n+10);++i)	t[i].clear(),dfn[i]=low[i]=fa[i]=deep[i]=top[i]=son[i]=col[i]=head[i]=vis[i]=pre[i]=0;
		solve();
	}
	return 0;
}
/*
2
4 4
LHLH
1 2
2 3
2 4
3 4
3 3
LHH
1 2
1 3
2 3
*/