Consider complex scenarios for `tt_at_path()<-` and related functions

[Melkiades]

          from the line 309 to the line 333, this is a complex scenario, thanks for considering all cases, @Melkiades , can you please add explicit test case for each scenario path

Originally posted by @shajoezhu in #1003 (comment)

[gmbecker]

@Melkiades could you put a bit more detail in here? What is the issue and was it solved/can it be simplified now that we're guaranteed pathability to all elements after #864 ?

[Melkiades]

I feel that this has been closed now. It was somewhat a reminder to expand the tests to more complex scenarios, i.e. when there were multiple identical pathways