for _ in range(int(input())):
    n,l = map(int,input().split())
    xy = sorted(tuple(map(int,input().split())) for _ in range(n))
    a = []; m = int(n**0.5)+1; print(n)
    for i in range(m): a += sorted(xy[i*m:(i+1)*m],key=lambda x:x[1])
    for x,y in a: print(x,y)