Programmatically way to determine if paho-mqtt processes queue is empty?

Programmatically way to determine if paho-mqtt processes queue completed? For example, if I call client.disconnect(), the on_disconnect call back may need a bit more time to complete, is there a way I can test for this?

Start by tracing client.disconnect() and the on_disconnect callback behavior in the client implementation. Determine how queued work and callback completion are represented, then define a documented, programmatic signal for completion and verify it with focused tests for disconnect timing.

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