Unit tests and upcoming ggplot2 4.0.0

[teunbrand]

Hi there,

We have been preparing for a new release of ggplot2 and during a reverse dependency check, it became apparent that the prospective ggplot2 3.5.0 would break ggparallel's units tests.

The main culprit is this pattern of unit testing:

ggparallel/tests/testthat/test-ggparallel.R

Lines 11 to 14 in 4b2ecd9

	load(system.file("mtcars.rda", package="ggparallel")) # loads object test_mtcars_plot
	built_saved <- ggplot2::ggplot_build(test_mtcars_plot)
	test <- ggparallel(list("gear", "cyl"), data=mtcars)
	build_now <- ggplot2::ggplot_build(test)

We don't recommend saving ggplot objects to disk, as it locks in internal code that may change between versions. While we attempt to keep the user-facing functions somewhat stable, we make no such promises about the internal code. For testing that plots still are the same, we recommend the vdiffr package.

Unfortunately, this issued showed up late on our radar and we plan to release ggplot2 3.5.0 on the 12th of February, so I do realise this is not entirely a timely notice.

[teunbrand]

We are now preparing ggplot2 4.0.0 and run into the same issue.
You can test your code with the development version of ggplot2 by installing it as follows:

# install.packages("pak")
pak::pak("tidyverse/ggplot2")

We aim to release the new ggplot2 version in about 2 weeks, and hope you can submit a fix to CRAN around that time. Hopefully this will inform you in a timely manner.

Best wishes,
Teun