import bisect
import sys
input = sys.stdin.readline
T = int(input())
for _ in range(T):
    N, L = map(int, input().split())
    DIV = int(L/(N**0.5))
    XY = [list(map(int, input().split())) for _ in range(N)]
    Z = [[[] for _ in range(DIV+1)] for _ in range(DIV+1)]
    D = [0 for _ in range(DIV+1)]
    D[DIV] = L+1
    for i in range(1, DIV):
        D[i] = int(L/DIV*i)
    for i in range(N):
        x, y = XY[i]
        xpos = bisect.bisect_left(D, x)
        ypos = bisect.bisect_left(D, y)
        Z[xpos][ypos].append(i)
    ans = []
    for i in range(DIV+1):
        for j in range(DIV+1):
            if i%2==0:
                k = j
            else:
                k = DIV-j
            for l in Z[i][k]:
                ans.append(XY[l])
    print(len(ans))
    for a in ans:
        print(*a)