Implement unit tests for the PubSub commands

[tishun]

Feature Request

Is your feature request related to a problem? Please describe

The unit tests coverage (class/method/line) for the io.lettuce.core.pubsub is 42% / 28% / 40%
A healthy amount is above 75%

Describe the solution you'd like

Implement unit tests for all the classes (minimum) to provide infrastructure
Implement unit tests for a healthy amount of coverage (best case)

Describe alternatives you've considered

We do have coverage by integration tests, but unit tests are run in insolation and could provide better whitebox testing

Teachability, Documentation, Adoption, Migration Strategy

N/A