dictionary 's .get( method tries to get the key value (1st parameter) and defaults to the second parameter if not found.
(Don't hesitate to reply to me if i'm reading this wrong ^^)

biggest

there are no guarantees...

indicate

If the adding step...

adding step

Beware the print ^^

Here too.

Why do you add it using storage_v1 first and then the using the multiplexer storage after that?
Why don't you always use the multiplexer storage?

Sorry if it's obvious but i don't see it ^^

Shouldn't there also be an adding tryout step with the readonly storage and then when you access this new content, it's not there (since it's readonly)?

What have I done? This is clearly not python. Indeed, that's simply get.

Here I'm cheating : as the multiplexer consider storage_v1 as a read-only storage, I wouldn't be able to add a content into it. So I bypass it and add the content directly into the storage without filter.

This way, I can test if the len of a multiplexer object storage detect all its storage and correctly return the number of files.

I've done it! The tests of the filters themselves are in test_multiplexer_filter.py. Here, I have no access to the read-only storage (only the initial storage, and the multiplexer).

Ah, yes...
I remember reading something like that in a docstring... Yes, in multiplexer_objstorage, add's docstring.
The content is considered added if all storages successfully add the content.
As the read-only won't be able to since it does nothing in that regard, then you cannot add it...
Thus the cheating step. ^^

Ok. Thanks!