Testing is a work in progress.

- As of Postfix 3.11 most new code is covered by tests.

- Many Postfix tests require building with shared=yes and dynamicmaps=no.
The shared=yes is needed so that test code can overrride internal
dependencies with mocks; the dynamicmaps=no is needed until there
is an easy way way to tell dynamicmaps support to not use the system
dynamicmaps.cf file.

- Historically, many tests in src/util, src/dns, and src/smtpd
are non-hermetic: they have dependencies on DNS or on local system
configuration.

- The PTEST test framework needs to be integrated; this fixed many many
non-hermetic tests in src/util and src/dns. That development stalled
after postfix-3.8-20220816-nonprod.