Has Kafka been tested manually or were automated tests also written?

Knowledge assessment of Dart on a scale from 1 to 5 depends on experience and depth of understanding of the language:

• 1 — basic knowledge, familiarity with syntax.
• 3 — confident proficiency, understanding of core concepts, experience in writing applications.
• 5 — deep understanding, experience in optimization, working with asynchronous operations, streams, creating custom libraries.

For example, if you can write applications in Flutter, understand async/await, work with streams, and architectural patterns, your score will be around 4-5.