Hi,
I know about the SETUPTOOLS_SCM_PRETEND_VERSION trick when it is used
in d/rules :
include /usr/share/dpkg/pkg-info.mk
export SETUPTOOLS_SCM_PRETEND_VERSION=$(DEB_VERSION_UPSTREAM)
dh-python do this automatically when python{,3}-setuptools-scm is in B-D.
I got around by turning d/tests/upstreamtestsuite to:
#!/bin/sh
set -e
SETUPTOOLS_SCM_PRETEND_VERSION=0.0.0 python3 setup.py test 2>&1
which worked because in fact the tests don't care about the version.
you can use "dpkg-parsechangelog -SVersion" or include /usr/share/dpkg/
pkg-info.mk + $DEB_VERSION_UPSTREAM here too.