https://pekko.apache.org/japi/pekko/snapshot/org/apache/pekko/stream/testkit/StreamTestKit.CompletedSubscription.html
StreamTestKit.CompletedSubscription
declaration: package: org.apache.pekko.stream.testkit, class: StreamTestKit, class: CompletedSubscription
https://pekko.apache.org/japi/pekko/snapshot/org/apache/pekko/stream/testkit/StreamTestKit.FailedSubscription$.html
StreamTestKit.FailedSubscription$
declaration: package: org.apache.pekko.stream.testkit, class: StreamTestKit, class: FailedSubscription$
https://pekko.apache.org/japi/pekko/snapshot/org/apache/pekko/stream/testkit/StreamTestKit.ProbeSource.html
StreamTestKit.ProbeSource
declaration: package: org.apache.pekko.stream.testkit, class: StreamTestKit, class: ProbeSource