[feature request] Make Kafka instrumentation more amenable to unit testing

[IGx89]

Component

OpenTelemetry.Instrumentation.ConfluentKafka

Is your feature request related to a problem?

I want to be able to unit test my application logic using mock IConsumer's instead of only being able to do E2E testing against a live Kafka instance.

I have code using the IConsumer.ConsumeAndProcessMessageAsync extension method and want to unit test it. I'm injecting an IConsumer mock into the DI container to facilitate that. That extension method throws an exception if consumer is not InstrumentedConsumer<TKey, TValue>, an internal class, preventing me from unit testing that code.

What is the expected behavior?

There are multiple possible solutions, including making InstrumentedConsumer public or removing the unnecessary consumer is not InstrumentedConsumer<TKey, TValue> check from the extension method.

Which alternative solutions or features have you considered?

Writing E2E tests (much slower and more complicated) or not testing my app logic, neither of which is appealing.

Additional context

No response

[github-actions]

Tagging component owner(s).

@g7ed6e

[IGx89]

I found another workaround that involves using reflection to set the "consumer" field on InstrumentedConsumer to my mock consumer. That unblocks me for now, but still would be nice to have a non-hacky solution.