iceberg-flink: Switch tests to JUnit5 + AssertJ-style assertions

[nastra]

Feature Request / Improvement

The goal is to switch all imports to JUni5 imports and to use AssertJ-style assertions

depends on #9077 #9078 #9079

Query engine

Flink

[ilyasahsan123]

hi @nastra , could you please assign this task to me?

[ilyasahsan123]

Hi @nastra,

I've submitted a pull request PR #9565 to migrate unittests to JUnit5 in Flink v1.16.

I'm considering sending multiple pull requests for this migration since there are a lot of classes involved. This way, the review process can be more manageable, and you can provide feedback more efficiently.

Let me know if this approach works for you.

Thanks!

[tomtongue]

@nastra If no one is assigned with this, could you assign this with me? I believe there are three remaining tasks like flink, spark other versions, data for the migration completion.