local function test_los()

local function test_losight_symmetry()

    end
  end
end
local function test_gridseegrid_symmetry()
  -- Clear messages to prevent them accumulating and forcing a --more--
  crawl.mesclr()
  -- Send the player to a random spot on the level.
  you.random_teleport()
  checks = checks + 1
  local you_x, you_y = you.pos()
  for y = -9, 9 do
    for x = -9, 9 do
      local px, py = x + you_x, y + you_y
      if (x ~= 0 or y ~= 0) and dgn.in_bounds(px, py) then
        local foreward = dgn.grid_see_grid(you_x, you_y, px, py)
        local backward = dgn.grid_see_grid(px, py, you_x, you_y)
        this_p = dgn.point(you_x, you_y)
        other_p = dgn.point(px, py)
        if not forward then
          you.moveto(px, py)
          local temp = this_p
          this_p = other_p
          other_p = temp
        end
        if forward ~= backward then
          dgn.grid(other_p.x, other_p.y, "floor_special")
          dgn.dbg_dump_map(FAILMAP)
          assert(false,
                 "grid_see_grid asymmetry detected (iter #" .. checks .. "): "
                   .. this_p .. " sees " .. other_p .. ", but not vice versa."
                   .. " Map saved to " .. FAILMAP)
        end
      end

      test_los()

      test_losight_symmetry()
    end
  end
  for lev_i = 1, nlevels do
    dgn.dbg_flush_map_memory()
    dgn.dbg_generate_level()
    for t_i = 1, tests_per_level do
      test_gridseegrid_symmetry()

end

end

LUAFN(dgn_grid_see_grid)
{
    COORDS(p, 1, 2);
    COORDS(q, 3, 4);
    return grid_see_grid(p, q);
}

    { "grid_see_grid", dgn_grid_see_grid },