Also successfully checked for Ubuntu 18.04 and R version 4.0.3.

Changes:

• Revision of the underlying data structure
• Roxygen documentation for main functionality
• Vignettes for quickstart and overview of available plots demonstrating the use of their corresponding plot functions
• Introduction of unit tests (package coverage >70%)
• Troubleshooting section covering potential issues during setup
• Finally: Extensive bug fixes and improvements (for a complete overview please check the Phabricator tasks)

Deleted branch bugfix/T26237-ImprovePerformance.

platform is output with Sys.info(); linux and Mac systems are equal and windows may differ

good idea!
otherwise you could use a platform dependent expect_equal but I think your idea is sufficient

After investing several hour trying different encodings, e.g. using raw strings, I still don't find a way to make this work. I also don't see a way of changing the source message, because it's originating from another package.

We should definitely keep it in the README.

would mention it there at least though because bootstrapping may be time consuming

don't think its necessary. there is anyway ordering applied to it in later stages.
otherwise ranking step (rank.aggregated.list()) could always do the ordering directly (then the test would check whether ordering is working). As mentioned before I avoided such change before the release because of (very unlikely) risk of breaking something in the first level hierarchy

Is the order of the rows relevant in any processing step? If not, the tests can be removed. Currently, I don't see a way making it work for both systems I have available for testing (Win10, R 3.6.3 and Ubuntu 18.04, R 4.0.3).

I do see those as well on Mac

R 4.0.2.
testthat previously 2.3.2, now 3.0.1.
the issue is however not connected to test_that I see that in the first 2 tests in aggregate-then-rank the ordering in the data set is not used but sorted

The platform might not be the (only) reason.
@wiesenfa: Which version of R and testthat are you using?