Provide tests on samples

[nmarquesantos]

Hey guys

It'd be great for me and other new people that are new to Spring Cloud Stream & Spring Cloud Function to be able to understand what is the best way to test the apps.

A lot of the kafka samples do not have any kind of testing besides a context load sanity check.

I'm unable to find anywhere in the documentation how I should test a Spring Cloud Function with Kafka underneath.

[altfatterz]

Here is a good example with embedded kafka: https://github.com/spring-cloud/spring-cloud-stream-samples/tree/master/testing-samples/test-embedded-kafka