import sys
input = sys.stdin.readline
t=int(input())
for _ in range(t):
  n,l=map(int,input().split())
  M=int(n**0.5)+1
  bucket=[[] for i in range(M)]
  xy=[]
  X=[]
  for i in range(n):
    x,y=map(int,input().split())
    xy.append((x,y))
  xy.sort()
  for i in range(n):
    x,y=xy[i]
    bucket[i*M//n].append((x,y)) 
  for i in range(M):
    if i&1:
      bucket[i].sort(key=lambda x:-x[1])
    else:
      bucket[i].sort(key=lambda x:x[1])
  ans=[]
  for i in range(M):
    for j in bucket[i]:
      ans.append(j)
  print(n)
  for i in ans:
    print(*i)