This was causing blender to segfault.
We now add create a new collection and link to the layer before adding
the new object
(also included unittests, and requires updated lib/tests)
test_evaluation_visibility_a failed before, but it is now fixed
test_evaluation_visibility_b passed before and was used as control to make sure it was not broken
Some tests may break Blender, which makes the entire unittest routine to fail.
They are now I isolate the tests into individual files
Kudos to Sybren Stüvel and Sergey Sharybin for the advice.
Note: at the moment test_link.py is failing (since a41bbfb7)
