#include<bits/stdc++.h>
using namespace std;
#define lowbit(i) (i&(-i))
const int mod=1e9+7,maxn=2e5+5,M=100005;
#define pb push_back
inline int read(){
	char ch=getchar();int x=0;bool f=0;
	for(;!isdigit(ch);ch=getchar())if(ch=='-')f=1;
	for(;isdigit(ch);ch=getchar())x=(x<<1)+(x<<3)+(ch^48);
	if(f==1)x=-x;return x;
}
int n,m,x,y,a[maxn],Rt,T,f[maxn][22],dep[maxn],vis[maxn];
char s[maxn];
int st[maxn],dfn[maxn],low[maxn],tot,idx,top,F;
vector<int>e[maxn],g[maxn];
int col[maxn],id[maxn];
int Lca(int x,int y){
    if(dep[x]<dep[y])swap(x,y);
    for(int i=20;i>=0;i--)if(dep[f[x][i]]>=dep[y])x=f[x][i];
    if(x==y)return x;
    for(int i=20;i>=0;i--)if(f[x][i]!=f[y][i])x=f[x][i],y=f[y][i];
    return f[x][0];
}
void tarjan(int x,int fa){
    dfn[x]=low[x]=++idx;st[++top]=x;
    f[x][0]=fa;dep[x]=dep[fa]+1;
    for(auto i:e[x]){
        if(dfn[i]){
            low[x]=min(low[x],dfn[i]);
            continue;
        }tarjan(i,x);
        low[x]=min(low[x],low[i]);
        if(low[i]>=dfn[x]){
            tot++;
            while(st[top+1]!=i){col[st[top]]=tot;top--;}
            id[tot]=x;
        }
    }
}
void dfs(int x,int fa){
    vis[x]=1;
    for(auto i:e[x])if(!vis[i]){
        dfs(i,x);
    }
    for(auto i:g[x]){
        int z=Lca(i,x);
        if(!dfn[i]||!dfn[x])continue;
        if(z==i||z==x)F=1;
        else if(col[x]==col[z]||col[i]==col[z])F=1;
        //else if(id[col[i]]==z||id[col[x]]==z)F=1;
    }
}
void solve(){
    n=read(),m=read();
    scanf("%s",s);
    tot=top=idx=F=0;
    for(int i=1;i<=m;i++){
        x=read(),y=read();
        if(s[x]!=s[y])e[x].pb(y),e[y].pb(x);
        else g[x].pb(y),g[y].pb(x);
    }
    tarjan(0,0);
    for(int j=1;j<=20;j++)
        for(int i=0;i<n;i++)
            f[i][j]=f[f[i][j-1]][j-1];
    dfs(0,0);
    if(F)puts("yes");
    else puts("no");
    for(int i=0;i<n;i++)e[i].clear(),g[i].clear(),dfn[i]=vis[i]=low[i]=col[i]=id[i]=dep[i]=0;
    for(int i=0;i<n;i++)for(int j=0;j<=20;j++)f[i][j]=0;
}
int main() {
    T=read();
    while(T--)solve();
    return 0;
}