I wasn't too sure about this cleanup because contact2 is using g_object_unref and contact1 is using g_assert_finalize_object to free the object, but I also tested using g_clear_object on both contact1 and contact2 instead of the current cleanup code and it ran through fine in valgrind too.

this should probably use !purple_strempty

Deleting this seems unnecessary

There's no need for the [class@Pruple.Account] here  its just redundant in the documentation.

clear object or unref on the second one should be fine.

reording this to the below should remove the need for the remove_all as that's just clearing the reference to the account that still exists in the manager. But if the manager is finalized first, it'll do its cleanup and unref the account as it should by itself.

g_assert_finalize_object(manager);
g_assert_finalize_object(account);

This should be marked as (out) and (optional), not (nullable).

Add g_assert_true(PURPLE_IS_CONTACT(contact1))? Right now they're just compared to each other, and could be NULL.