Add a basic test of apertis-pkg-pull-updates functionality

Try to download an update for dash from Buster, given a repository
with a version from Lenny. Don’t try to check when exactly is in the
update, as versions may change, but verify a tarball has been imported.

Signed-off-by: Andrej Shadura <andrew.shadura@collabora.co.uk>

.gitlab-ci.yml

@@ -127,6 +127,16 @@ test-package-source-builder:
     name: $CI_REGISTRY_IMAGE/${RELEASE}-package-source-builder:${TEST_TAG}
     entrypoint: [ "" ]
   script:
+    - git clone https://gitlab.apertis.org/infrastructure/test-data/fixture-dash-non-updated
+    - ": Verify we can pull updates from Buster"
+    - cd fixture-dash-non-updated
+    - apertis-pkg-pull-updates --upstream=buster --mirror https://deb.debian.org/debian
+    - head -n 10 debian/changelog
+    - git log --graph --oneline
+    - pristine-lfs list
+    - test "$(git tag --list 'debian/*' | wc -l)" = 2
+    - test "$(pristine-lfs list | wc -l)" = 2
+    - cd ..
     - git clone https://gitlab.apertis.org/infrastructure/test-data/fixture-dash-unmodified
     - ": Verify we correctly detect when there are no local changes and use the co0 suffix"
     - cd fixture-dash-unmodified