minetest.register_chatcommand("t", {
    params = "";
    description = "Test";
    func = function ( name, param )
        local formspec = "size[4,4]"..
            "image_button[0,0;2,2;default_wood;test;Test]"..
            "image[2,0;2,2;default_wood]";
        minetest.show_formspec(name, "test", formspec);
    end;
})