#include <algorithm>
#include <cstdio>

constexpr int MAXN = 1000000 + 2;

int pos[MAXN << 1];

char a[MAXN << 1], b[MAXN], c[MAXN], ans[MAXN];

int main() {
    int T;
    scanf("%d", &T);

    while (T --) {
        int n, m;
        scanf("%d%d%s", &n, &m, a);

        if (n < m) {
            std::swap(n, m);
        }

        for (int i = 0; i <= n; i ++) {
            b[i] = c[i] = false;
        }
        for (int i = 1; i <= n + m; i ++) {
            pos[i] = MAXN << 1;
        }
        for (int i = 0, cnt = 0; i < n + m; i ++) {
            if (a[i] == '1') {
                pos[++ cnt] = i;
            }
        }

        for (int i = 0, p1 = n, p2 = m, cnt = 0; i < n + m; i ++) {
            if (a[i] == '0') {
                (p2 ? p2 : p1) --;
            } else {
                cnt ++;

                if (pos[cnt + p1 - p2] - i - p1 >= 0) {
                    b[-- p1] = true;
                } else {
                    c[-- p2] = true;
                }
            }
        }

        for (int i = 0, carry = 0; i <= n; i ++) {
            ans[i] = b[i] ^ c[i] ^ carry;
            carry = b[i] + c[i] + carry > 1;
        }

        int p = n;

        while (p && !ans[p]) {
            p --;
        }

        for (int i = p; i >= 0; i --) {
            putchar(ans[i] ^ '0');
        }
        putchar('\n');
    }

    return 0;
}