Review and improve developer-run integration testing instructions

As an contributing developer
I want clear instructions on how to run the various integration tests

AC:
* a reviewer is able to follow the instructions and run all the applicable integration tests

The issue does not name a documentation file or integration-test entry point. Review the repository's existing test instructions and integration-test setup first, then document how a developer can run all applicable integration tests. Done means a reviewer can follow the instructions and run the complete applicable integration-test set.

索引モデルが issue の本文から書いたものです。