Lua __mode test

local test = function (mode, t, k, v, k2, v2)
    print('', 'k == ' .. tostring(k), 'v == ' .. tostring(v))
   print('', 'k2 == ' .. tostring(k2), 'v2 == ' .. tostring(v2))
    collectgarbage()
    for k,v in pairs(t) do print('',k,v) end
    print('')
end
local testmt = function (mode)
    local t = setmetatable({},{__mode = mode})
    local k, k2, v, v2 = {},{},{},{}
    t[k] = v
    t[k2] = v2
    t[v] = k2
    t[v2] = k

    print('testing mode ' .. mode)

    table.insert(t,k); print('t[1] == k')
    table.insert(t,k2); print('t[2] == k2')
    table.insert(t,v); print('t[3] == v')
    table.insert(t,v2); print('t[4] == v2')

    test(mode,t,k,v,k2,v2)

    k = nil
    test(mode,t,k,v,k2,v2)

    v2 = nil
    test(mode,t,k,v,k2,v2)

    k2 = nil
    test(mode,t,k,v,k2,v2)

    v = nil
    test(mode,t,k,v,k2,v2)
    print('mode ' .. mode .. ' complete.')
    print('')
end

for _,v in ipairs{'k','v','kv'} do testmt(v) end