MOD = 998244353i64

read_line.to_i.times do
  solve()
end

def solve
  n, l = read_line.split.map(&.to_i)
  xys = Array.new(n) { read_line.split.map(&.to_i) }
  mo = Mo.new(l, (l + 1 + 499) // 500)
  xys.each do |xy|
    mo.add_query(xy[0], xy[1])
  end
  mo.build
  puts n
  mo.each do |x, y, _|
    puts "#{x} #{y}"
  end
end

class Mo
  include Enumerable(Tuple(Int32, Int32, Int32))

  def initialize(@n : Int32, @bucket_size : Int32)
    @bucket = Array(Array(Int32)).new((@n + @bucket_size - 1) // @bucket_size) { [] of Int32 }
    @qs = Array(Tuple(Int32, Int32)).new
  end

  def add_query(l : Int32, r : Int32)
    @bucket[l // @bucket_size] << @qs.size
    @qs << {l, r}
  end

  def build
    @bucket.size.times do |i|
      @bucket[i].sort_by! { |qi| @qs[qi][1] }
      if i % 2 != 0
        @bucket[i].reverse!
      end
    end
  end

  def each
    @bucket.each do |b|
      b.each do |qi|
        yield ({@qs[qi][0], @qs[qi][1], qi})
      end
    end
  end
end