But those method names are still hard to relate to the business cases your customer requested. So you implemented something for some reason; your code and methods tell you what you implemented but not why... Why did you use a tree? I read your top level code and think ; dude, that would have been so much simpler and faster using a Wobble instead of a Tree! Then I try that and it turns out it has to be a Tree; you went through the same process, did not tell me why and I lost a day retrying. For instance.
(assuming, which you should always assume imho, that you left the company many years ago when this event occurs)
If I wrote an explanation then what would check that explanation? Maybe I write "we use a Tree instead of a Wobble because Wobble doesn't support the APIs we need". But then maybe when you come to work on it, it turns out that the current version of Wobble does support those APIs. Maybe it's actually better at them than Tree. Whereas if I have a unit test around Tree that exercises the kind operations that we need to do, then you can just try dropping Wobble in there and see for yourself whether it works or not.
(assuming, which you should always assume imho, that you left the company many years ago when this event occurs)