Adopt dedicated AssertJ assertions for more expressive test failure messages

[timtebeek]

Noticed that there were some instances where AssertJ wasn't used to it's full expressive potential, so I ran our AssertJ best practices recipe (via) to adopt dedicated assertions. This should help the message when an assertion fails, such that it's not "expected true but was false", but instead something like "expected collection to contain "apple", but was ["banana"]".

-assertThat(objectIdentities.size()).isEqualTo(1);
+assertThat(objectIdentities).hasSize(1);

-assertThat(objects.contains("apple")).isTrue();
+assertThat(objects).contains("apple");

These are mostly automated changes with some manual fixes; I recommend a squash merge if possible. I hope this is appreciated! :)

[jzheaux]

Thanks, @timtebeek! This is very helpful.

I've left a comment inline about one of the changes.

Also, if you wish at this point, you are welcome to squash your commits to a single commit.

[timtebeek]

Glad to hear you think it's helpful! I've fixed my manual mistake and think we should be good for a (squash) merge.

I'd noticed another small possible improvement, which is why it's fun for me to do these PRs; can circle back on that in the future if that's appreciated; should make for a smaller PR by then.

[timtebeek]

Anything else you'd like to see before a squash merge @jzheaux ? I'd hope to get this in before there's merge conflicts if at all possible, but understand this is far from a critical change.

[timtebeek]

Gone ahead and merged the followup commits into the first one such that it's now just a single commit; hope that helps!

[jzheaux]

Thanks, @timtebeek! This is now merged into main.