and "xyz" and single letters that are used in the tests. The test suite
expects the login to have a gecos name; I think it will now run if the
gecos field is empty but there may be anomalies.
+ The login must not contain a dash or an equal sign. (Otherwise some tests
+ about local_from_{suffix,prefix} will fail.)
(4) The directory into which you unpack the test suite must be accessible by
the Exim user, so that code running as exim can access the files therein.