#include<iostream>
using namespace std;
int main()
{
    int t;
    cin>>t;

    while(t--){
        long long n,k;
        cin>>n>>k;

        string s;
        cin>>s;

        int left=0, right = 0, count=0, ones=0;

        while(right<n){
            if(s[right]=='0'){
                count++;
            }
            while(count>k){
                    if(s[left]=='0'){
                        count--;
                    }
                    left++;
            }

            ones = max(ones, right-left+1);
            right++;
        }

        cout<<ones<<"\n";
    }
}