* `SftpSessionFactoryTests.concurrentGetSessionDoesntCauseFailure()`
may not report properly into an `ArrayList` from another thread.
Use `asyncTaskExecutor.submitCompletable()` instead and deal with their result afterward.
* Use `CompletableFuture` for the `TcpListener` logic in the `FailoverClientConnectionFactoryTests.failoverAllDeadAfterSuccess()`
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