T = int(input())
for _ in range(T):
    N, X = map(int, input().split())
    C = list(map(int, input().split()))
    ans = 0
    for c in C:
        if X >> c & 1 == 0:
            mask = ((1 << c) - 1) & X
            ans = max(ans, ((X | (1 << c)) ^ mask) - X)
    print(2 * ans)