T = int(input())
for _ in range(T):
    K = int(input())
    S = input().strip()
    N = len(S)
    if S[0] == '0':
        val = int(S, 2)
        if K >= N:
            val_shifted = 0
        else:
            val_shifted = val >> K
        S_result = bin(val_shifted)[2:].zfill(N)
    else:
        val = int(S, 2) - (1 << N)
        if K >= N:
            val_shifted = -1
        else:
            val_shifted = val >> K
        val_shifted &= (1 << N) - 1
        S_result = bin(val_shifted)[2:].zfill(N)
    print(S_result)