[exim] testing login from the command line

Is there a way to get exim to test a dovecot login from the command line?

The background to this is when I upgrade from 4.93.0.3 ro 4.94 all
logins fail with the log file reporting:

2020-07-05 09:10:46 dovecot_plain authenticator failed for
([192.168.0.165]) [192.168.0.165]: 435 Unable to authenticate at
present: unable to connect to UNIX socket
(/var/run/dovecot/auth-client): Permission denied

If I write a program to connect to that socket it works just fine, as
any user, and exim-4.93.0.3 has no issues either, so something weird is
going on and I want to debug it directly using the exim-4.94 binary, but
to do so I need to get it to attempt the dovecot login.

Many thanks

Chris Gerhard