#include<bits/stdc++.h>

using namespace std;

namespace Fread {
	const int SIZE=1<<21;char buf[SIZE],*S,*T;
	inline char getchar() {if(S==T){T=(S=buf)+fread(buf,1,SIZE,stdin);if(S==T)return '\n';}return *S++;}
}
namespace Fwrite {
	const int SIZE=1<<21;
	char buf[SIZE],*S=buf,*T=buf+SIZE;
	inline void flush(){fwrite(buf,1,S-buf,stdout);S=buf;}
	inline void putchar(char c){*S++=c;if(S==T)flush();}
	struct POPOSSIBLE{~POPOSSIBLE(){flush();}}ztr;
}
#define getchar Fread :: getchar
#define putchar Fwrite :: putchar
namespace Fastio{
	struct Reader{
	    template<typename T>
    	Reader& operator >> (T& x) {
        	char c=getchar();T f=1;
        	while(c<'0'||c>'9'){if(c=='-')f=-1;c=getchar();}x=0;
        	while(c>='0'&&c<='9'){x=x*10+(c-'0');c=getchar();}x*=f;
	        return *this;
    	}
	    Reader& operator >> (char& c) {c=getchar();while(c==' '||c=='\n')c=getchar();return *this;}
	    Reader(){}
	}cin;
	struct Writer{
	    template<typename T>
	    Writer& operator << (T x) {
	        if(x==0){putchar('0');return *this;}
	        if(x<0){putchar('-');x=-x;}
	        static int sta[45];int top=0;
	        while(x){sta[++top]=x%10;x/=10;}
	        while(top){putchar(sta[top]+'0');--top;}
	        return *this;
    	}
    	Writer& operator << (char c) {putchar(c);return *this;}
    	Writer& operator << (const char* str){int cur=0;while(str[cur])putchar(str[cur++]);return *this;}
    	Writer(){}
	}cout;
}
#define endl '\n'
#define cin Fastio :: cin
#define cout Fastio :: cout

const int B=20;
const int N=6e5+10;
struct edge{
	int to,ne;
	edge(int to=0,int ne=0):
		to(to),ne(ne){;}
}a[N<<1];
int h[N],cnt,n,m,bel[N],flag[N],tot,stk[N],Top,dfn[N],T,col[N];
int X[N],Y[N],f[N][B+1],root[N],low[N],idx,dep[N];
vector < int > v[N];vector < int > p[N];char in;

/*
	1.图不一定连通，所以树也不一定连通。
	2.tot的初值
*/

void clear(){
	for(int i=1;i<=m;++i) X[i]=Y[i]=0;
	for(int i=1;i<=tot;++i){
		h[i]=bel[i]=flag[i]=stk[i]=dfn[i]=root[i]=low[i]=dep[i]=col[i]=0;
		for(int j=0;j<=B;++j) f[i][j]=0;
		v[i].clear();p[i].clear();
	}
	for(int i=1;i<=cnt;++i) a[i]=edge();
	cnt=tot=Top=idx=0;
}

inline void add(const int x,const int y){a[++cnt]=edge(y,h[x]);h[x]=cnt;}

void tarjan(const int x,int rt){
	dfn[x]=low[x]=++idx;stk[++Top]=x;
	if(x==rt&&v[x].empty()){--Top;p[++tot].emplace_back(x);if(!flag[x]) bel[x]=tot;return ;}
	int ct=0,tmp;
	for(int i:v[x]){
		if(!dfn[i]){
			tarjan(i,rt);
			low[x]=min(low[x],low[i]);
			if(low[i]>=dfn[x]){
				++ct;if(x!=rt||ct>1) flag[x]=1,bel[x]=0;++tot;
				if(!flag[x]) bel[x]=tot;
				p[tot].emplace_back(x);
				while(stk[Top+1]!=i){
					tmp=stk[Top--];
					p[tot].emplace_back(tmp);
					if(!flag[tmp]) bel[tmp]=tot;
				}
			}
		}else low[x]=min(low[x],dfn[i]);
	}
}


void dfs(int x,int y,int rt){
	f[x][0]=y;root[x]=rt;dep[x]=dep[y]+1;
	for(int i=1;i<=B;++i) f[x][i]=f[f[x][i-1]][i-1];
	for(int i=h[x];i;i=a[i].ne) if(a[i].to!=y) dfs(a[i].to,x,rt);
}

inline int LCA(int x,int y){
	if(dep[x]<dep[y]) swap(x,y);
	for(int i=B;~i;--i) if(dep[f[x][i]]>=dep[y]) x=f[x][i];
	if(x==y) return x;
	for(int i=B;~i;--i) if(f[x][i]!=f[y][i]){x=f[x][i];y=f[y][i];}
	return f[x][0];
}

int main(){
	//freopen("travel.in","r",stdin);
	//freopen("travel.out","w",stdout);
	cin>>T;
	while(T--){
		cin>>n>>m;tot=n;int fg=0;
		for(int i=1;i<=n;++i){cin>>in;col[i]=(in=='H');}
		for(int i=1;i<=m;++i){
			cin>>X[i]>>Y[i];
      ++X[i], ++Y[i];
			if(col[X[i]]!=col[Y[i]]){
				v[X[i]].emplace_back(Y[i]);
				v[Y[i]].emplace_back(X[i]);
			}
		}
		for(int i=1;i<=n;++i) if(!dfn[i]) tarjan(i,i);
		for(int i=n+1;i<=tot;++i) for(auto j:p[i]) if(flag[j]){add(j,i);add(i,j);}
		for(int i=1;i<=n;++i) if(flag[i]) bel[i]=i;
		dfs(bel[1],0,bel[1]);
		for(int i=1;i<=m;++i){
			if(col[X[i]]!=col[Y[i]]) continue;
			if(X[i]==Y[i]) continue;
			int x=bel[X[i]],y=bel[Y[i]];
			if(root[x]!=bel[1]||root[y]!=bel[1]) continue;
    		if(flag[x]&&x!=1) x=f[x][0];
    		if(flag[y]&&y!=1) y=f[y][0];
			int z=LCA(x,y);if((z==x)||(z==y)) fg=1;
//			cout<<flag[1]<<' '<<bel[1]<<' '<<x<<' '<<y<<' '<<z<<endl;
		}
		cout<<(fg?"yes\n":"no\n");
		clear();
	}
	return 0;
}