If anyone else has problems compiling mapnik, I needed a horrifying workaround:

./bin/use maps

# ... clone snapshot ...

rsync -av ../kartotherian/packages/snapshot/{node_modules,package-lock.json} .

docker run --rm -v $(pwd):/srv/snapshot -it docker_kartotherian bash

In other words, steal node_modules as installed by lerna, then work inside the container so that tool versions are pinned.

Continuing my workaround exploration... The only way I found to install test dependencies was this crazy command, also pulling in some external dependencies that the repo requires because it's naughty:

./clean_node_modules.sh
lerna bootstrap
cd packages/snapshot

npm i -D eslint@^4.19.1 eslint-config-kartotherian@0.0.5 jest@^27.3.1 mocha@^5.0.4 @wikimedia/err@1.0.3 @wikimedia/kartotherian-input-validator@1.0.2

Change 736502 had a related patch set uploaded (by Awight; author: Awight):

[mediawiki/services/kartotherian@wmde-maps-revid] [WIP] Skeletal test for revid pass-through

https://gerrit.wikimedia.org/r/736502

The tests are written, but due to the mapnik dependency I haven't been able to upstream or add to CI.

I mentioned today that the changes should be upstreamed to the independent "snapshot" repo, but now I see that it has officially been moved to live in kartotherian/packages/snapshot, so the patch can stand as it is.

Change 736502 merged by jenkins-bot:

[mediawiki/services/kartotherian@wmde-maps-revid] Test for revid pass-through

https://gerrit.wikimedia.org/r/736502