[Feature] Refactor Kafka-CDC tests

[yuzelin]

Search before asking

• [X] I searched in the issues and found nothing similar.

Motivation

This is an umbrella issue. Kafka cdc tests are complicated. There are many test cases, we can extract common parts to clean the code. Besides, Kafka cdc contains four formats now, some tests are redundant.

Solution

No response

Anything else?

No response

Are you willing to submit a PR?

• [X] I'm willing to submit a PR!