#include<bits/stdc++.h>
using namespace std;
const int MAXN=2e5+7;
struct node{
	string str;
}a,tot,mine,it;
int l1[MAXN],l2[MAXN],l3[MAXN],n,k,len;
node minu(node x,node y)
{
	if(x.str.size()<y.str.size())
		return x;
	if(x.str.size()>y.str.size())
		return y;
	if(x.str<y.str)
		return x;
	else
		return y;
}
node operator + (const node &x,const node &y)
{
	node ans;
	ans.str="";
	memset(l3,0,sizeof(l3));
	int len1=x.str.size(),len2=y.str.size(),len3;
	for(int i(1);i<=len1;++i)
		l1[len1-i+1]=x.str[i-1]-'0';
	for(int i(1);i<=len2;++i)
		l2[len2-i+1]=y.str[i-1]-'0';
	len3=max(len1,len2);
	for(int i(1);i<=max(len1,len2);++i)
	{
		if(i>len1)
		l1[i]=0;
		if(i>len2)
		l2[i]=0;
		l3[i]+=(l1[i]+l2[i])%10;
		l3[i+1]+=(l1[i]+l2[i])/10;
	}
	while(l3[len3])
	{
		l3[len3+1]+=l3[len3]/10;
		l3[len3]%=10;
		++len3;
	}
	len3--;
	while(l3[len3]>=10)
	{
		l3[len3+1]+=l3[len3]/10;
		l3[len3]%=10;
		len3++;
	}
	for(int i(len3);i>=1;--i)
	{
		ans.str+=l3[i]+'0';
		if(ans.str[len3-i]<'0'||ans.str[len3-i]>'9')
			printf("ccccccccccc");
	}
	return ans;
}
void dfs(node s,int x,int cnt)
{
	if(x>=n||cnt>k)
		return ;
	if(cnt==k)
	{
		it.str=a.str.substr(x,MAXN);
		mine=minu(mine,it+s);
		return ;
	}
	it.str=a.str.substr(x,len-1);
	dfs(s+it,x+len-1,cnt+1);
	it.str=a.str.substr(x,len);
	dfs(s+it,x+len,cnt+1);
	it.str=a.str.substr(x,len+1);
	dfs(s+it,x+len+1,cnt+1);
	it.str=a.str.substr(x,MAXN);
	mine=minu(mine,it+s);
	return ;
}
int main()
{
	int t;
	scanf("%d",&t);
	while(t--)
	{
		scanf("%d%d",&n,&k);
		cin>>a.str;
		mine.str=a.str;
		len=n/(k+1);
		tot.str=a.str.substr(0,len-1);
		dfs(tot,len-1,1);
		tot.str=a.str.substr(0,len);
		dfs(tot,len,1);
		tot.str=a.str.substr(0,len+1);
		dfs(tot,len+1,1);
		cout<<mine.str<<endl;
	}
	return 0;
 }