Under `test_environment` we store Dockerfiles defining three computing environments
for testing mapMCDA:
-`oldrel`: the latest major release of R,
-`release`: the current release of R
-`devel`: the next major release, under development
The images are built locally (see Makefile) and pushed to the [Docker registry
at Forgemia](https://forgemia.inra.fr/umr-astre/mapMCDA/container_registry).
These images are used for Continuous Integration testing ([`.gitlab-ci.yml`](https://forgemia.inra.fr/umr-astre/mapMCDA/-/blob/master/.gitlab-ci.yml)).
The images are based on the [Rocker-versioned
images](https://hub.docker.com/r/rocker/r-ver) which in turn are based on either
Debian (for R <4.0)orUbuntu(forR>= 4.0).
For `oldrel`, package dependencies are installed from a CRAN snapshot at the
last date that particular R version was current. The result is an old R version
with contemporary versions of R-packages (i.e. not latest versions).