Quibble and Docker support downloading a complete environment and running all tests. This task requests support to download a complete environment but allow for a local repository, such as MobileFrontend, to be overridden and to run only tests for that environment. The proposed syntax is as follows:
```
docker run -it --rm \
-v "$(pwd)"/cache:/cache \
-v "$(pwd)"/log:/workspace/log \
-v "$(pwd)"/ref:/srv/git:ro \
-v "$(pwd)"/src:/workspace/src \
-v "$(pwd)"/vagrant/mediawiki/extensions/MobileFrontend:/workspace/src/mediawiki/extensions/MobileFrontend \
docker-registry.wikimedia.org/releng/quibble-stretch:latest \
--test extensions/MobileFrontend
```
In the above example, two changes occur:
# Use the local copy of MobileFrontend specified. Don't download this extension.
# Only run tests for MobileFrontend.
The use case is for testing local patches developed in a local Vagrant instance.