import sys

sys.setrecursionlimit(200005)
# sys.set_int_max_str_digits(200005)
int1 = lambda x: int(x)-1
pDB = lambda *x: print(*x, end="\n", file=sys.stderr)
p2D = lambda x: print(*x, sep="\n", end="\n\n", file=sys.stderr)
def II(): return int(sys.stdin.readline())
def LI(): return list(map(int, sys.stdin.readline().split()))
def LLI(rows_number): return [LI() for _ in range(rows_number)]
def LI1(): return list(map(int1, sys.stdin.readline().split()))
def LLI1(rows_number): return [LI1() for _ in range(rows_number)]
def SI(): return sys.stdin.readline().rstrip()

dij = [(0, 1), (-1, 0), (0, -1), (1, 0)]
# dij = [(0, 1), (-1, 0), (0, -1), (1, 0), (1, 1), (1, -1), (-1, 1), (-1, -1)]
# inf = -1-(-1 << 31)
inf = -1-(-1 << 62)

# md = 10**9+7
md = 998244353

from collections import defaultdict

def solve():
    n,l=LI()
    xy=LLI(n)
    h = round(n**0.5)
    i2xy=defaultdict(list)
    for x,y in xy:
        i=x//h
        i2xy[i].append((x,y))
    ans=[]
    for i in sorted(i2xy):
        i2xy[i].sort(key=lambda x:x[1])
        ans+=i2xy[i]

    print(len(ans))
    for x,y in ans:print(x,y)

for _ in range(II()):solve()