#include<bits/stdc++.h>
#define LL long long
using namespace std;
const LL mod=487696949LL;
const LL mod2=127372829LL;
int T,n,k;
string s;
LL has[1000006],base[1000006];
LL has2[1000006],base2[1000006];
map<LL, bool> vis,vis2;
LL ans;

void initH(string s)
{
    has[0]=s[0]-'0';
    base[0]=1;
    has2[0]=s[0]-'0';
    base2[0]=1;
    for(int i=1;i<s.length();i++)
    {
        has[i]=((has[i-1]*2)%mod+s[i]-'0')%mod;
        has2[i]=((has2[i-1]*2)%mod2+s[i]-'0')%mod2;
        base2[i]=base2[i-1]*2;base2[i]%=mod2;
        base[i]=base[i-1]*2;base[i]%=mod;
    }
    return ;
}

LL getSub(int qi, int len)
{
    int ed=qi+len-1;
    LL ret;
    if(qi==0)
    {
        ret=has[ed];
    }
    else
    {
        ret=(has[ed]-has[qi-1]*base[len]%mod)%mod;
    }
    // printf("qi=%d ed=%d ret=%lld\n",qi,ed,ret);
    return (ret+mod)%mod;
}
LL getSub2(int qi,int len)
{
    int ed=qi+len-1;
    LL ret;
    if(qi==0)ret=has2[ed];
    else ret=(has2[ed]-has2[qi-1]*base2[len]%mod2)%mod2;
    return (ret+mod2)%mod2;
}
void printS(LL x)
{
    vector<int> res;
    res.clear();
    while(x)
    {
        if(x&1)res.push_back(1);
        else res.push_back(0);
        x>>=1;
    }
    while(res.size()<k)res.push_back(0);
    for(int i=res.size()-1;i>=0;i--)printf("%d",res[i]);
    printf("\n");
}

int main()
{
    scanf("%d",&T);
    while(T--)
    {
        vis.clear();
        scanf("%d%d",&n,&k);
        cin>>s;
        for(int i=0;i<s.length();i++)s[i]=(s[i]=='1'? '0':'1');
        initH(s);
        // for(int i=0;i<s.length();i++)printf("%lld\n",has[i]);
        for(int i=0;i+k-1<n;i++)
        {            
            LL tem=getSub(i,k);
            LL tem2=getSub2(i,k);
            // printf("tem=%lld\n",tem);
            vis[tem]=1;
            vis2[tem2]=1;
        }
        int fl=0,mx=0;
        for(int i=0;i<k;i++)mx=((mx*2)%mod+1)%mod;
        for(ans=0;ans<=mx;ans++)
        {
            if((!vis[ans])||(!vis2[ans])){fl=1;break;}
        }
        // printf("ans=%lld\n",ans);
        printf(fl?"YES\n":"NO\n");
        if(fl)printS(ans);
    }
}