How to trace client sql requests?

I have a situation with a Rails project where test data in
mysteriously "disappearing" in the middle of a test run.  I would
like to see the exact SQL of all client requests issued against a
single table during a fixed time span.

How can I best accomplish this in PostgreSQL?

#client_min_messages = notice
#log_min_messages = notice
#log_min_duration_statement = -1
...
#log_duration = off

Which of these, if any, should I alter; and to what?  Am I
constrained to system wide logging or can this be enabled by
database?

Regards,

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