T = int(input())
for _ in range(T):
    N, X = map(int, input().split())
    c = list(map(int, input().split()))
    ans = 0
    d = []
    for i in range(N):
        for j in range(-1, 60):
            t = 2**j
            if j == -1:
                t = 0
            if ((X + t) & (2**c[i])) != 0:
                d.append(t)
                break
    # print(d)
    print(max(d)*2)

# for i in range(10):
#     print(f"{i & 8 = }, {i = }")