Testing code immediately invoked in a script

I'm currently writing unit tests for a lua mod library using Busted. The file in question defines a module with some functions, then calls one of those functions at the bottom to initialize itself.

The problem I'm finding is that Busted appears to be evaluating the required-in file twice.

Test

it('does a thing', function()
    -- Some setup, replacing globals etc
    require('items')
    assert.are_equal(2, #Items._registry)
end)

Module

Items = { _registry = {} }
function Items.do_some_stuff() end
function some_util_func() end
function load_registry()

load_registry()

As you can see, although I've simplified the code and names, the structure is nothing out of the blue (as I understand.)

The test will always fail, because #Items._registry is always 0 (and dumping to the console verifies that). I tried printing inside the method and found it printed twice; then I tried using debug.traceback at the top of that unction and found the below. As you can see, the stack traceback is printing twice, suggesting the code is being evaluated twice.

Is this something anybody else has come across? Am I structuring my test wrong for this scenario? Or this a bug?

---

stack traceback:
    ./stdlib/trains/trains.lua:96: in function 'register_all_trains'
    ./stdlib/trains/trains.lua:109: in main chunk
    [C]: in function 'require'
    spec/trains/train_module_load_spec.lua:50: in function <spec/trains/train_module_load_spec.lua:39>
    [C]: in function 'xpcall'
    /usr/local/share/lua/5.2/busted/core.lua:178: in function 'safe'
    /usr/local/share/lua/5.2/busted/init.lua:40: in function 'executor'
    /usr/local/share/lua/5.2/busted/core.lua:312: in function </usr/local/share/lua/5.2/busted/core.lua:312>
    [C]: in function 'xpcall'
    /usr/local/share/lua/5.2/busted/core.lua:178: in function 'safe'
    ...
    /usr/local/share/lua/5.2/busted/core.lua:312: in function 'execute'
    /usr/local/share/lua/5.2/busted/block.lua:155: in function 'execute'
    /usr/local/share/lua/5.2/busted/init.lua:7: in function 'executor'
    /usr/local/share/lua/5.2/busted/core.lua:312: in function </usr/local/share/lua/5.2/busted/core.lua:312>
    [C]: in function 'xpcall'
    /usr/local/share/lua/5.2/busted/core.lua:178: in function 'safe'
    /usr/local/share/lua/5.2/busted/core.lua:312: in function 'execute'
    /usr/local/share/lua/5.2/busted/execute.lua:58: in function 'execute'
    /usr/local/share/lua/5.2/busted/runner.lua:174: in function </usr/local/share/lua/5.2/busted/runner.lua:11>
    /usr/local/lib/luarocks/rocks/busted/2.0.rc12-1/bin/busted:3: in main chunk
    [C]: in ?
stack traceback:
    ./stdlib/trains/trains.lua:96: in function 'register_all_trains'
    ./stdlib/trains/trains.lua:109: in main chunk
    [C]: in function 'require'
    spec/trains/trains_spec.lua:15: in main chunk
    [C]: in function 'xpcall'
    /usr/local/share/lua/5.2/busted/core.lua:178: in function 'safe'
    /usr/local/share/lua/5.2/busted/block.lua:146: in function 'execute'
    /usr/local/share/lua/5.2/busted/init.lua:7: in function 'executor'
    /usr/local/share/lua/5.2/busted/core.lua:312: in function </usr/local/share/lua/5.2/busted/core.lua:312>
    [C]: in function 'xpcall'
    /usr/local/share/lua/5.2/busted/core.lua:178: in function 'safe'
    /usr/local/share/lua/5.2/busted/core.lua:312: in function 'execute'
    /usr/local/share/lua/5.2/busted/execute.lua:58: in function 'execute'
    /usr/local/share/lua/5.2/busted/runner.lua:174: in function </usr/local/share/lua/5.2/busted/runner.lua:11>
    /usr/local/lib/luarocks/rocks/busted/2.0.rc12-1/bin/busted:3: in main chunk
    [C]: in ?