#include <iostream>
#include <vector>
#include <string>
#include <algorithm>

using namespace std;

int x(string &m, int n) {
    int o = m.length();
    int p = 0, q = 0, r = 0,s = 0;

    while (q < o) {
        if (m[q] == '0') {
           s++;
        }

        while (s > n) {
            if (m[p] == '0') {
               s--;
            }
            p++;
        }

        r = max(r, q - p + 1);
        q++;
    }

    return r;
}

int main() {
    int s;
    cin >> s;

    while (s--) {
        int t, u;
        string v;
        cin >> t >> u;
        cin >> v;

        int w = x(v, u);
        cout << w << endl;
    }

    return 0;
}