fix: server broken tests

[jadok]

Fix unit tests on the server package broken due to wrong typings.

You will find a trick by setting to any the type of Bus to make available a private membre of the class. Another weird trick: { id: 'test_client', emit: jest.fn() } as unknown as Socket to cast the object to a Socket type.

The whole server package has unit test working.

[jadok]

For an unknown reason, travis failled to run yarn run fmt:check which succeed on my environment (windows 8, node 10.15)