Not able connect with Rest High Level Client in ESIntegTestCase of ElasticSearch 7.0.0

You can not run elasticsearch embedded. Read this blog post.

Note that to run integration tests (not unit tests) you would probably prefer running that in something close to a production environment, like a real elasticsearch server instance. I shared some ideas about integration testing in this thread: In memory testing with RestHighLevelClient

Also this sample project shows how to use Elasticsearch Test Classes: