R 4.0.0 breaks current tests

[TimTaylor]

For info - a few of the tests now error due to the the matrix class now inheriting from array in R 4.0.0. This mainly affects the tests that compare to the rds files generated under an old version of R but also one of the tests in test_cumulate.

[thibautjombart]

Thanks for flagging this. I will get to it as soon as I get a chance.

[TimTaylor]

If you want to keep the tests for older versions of R then a quick hacky fix is to add something like

attributes(pred_1)$class <- attributes(pred_1)$class[(1:2)]

in the tests where the projections utilise rds files.

However given that this is just for tests and won't break any code, it may be better to just update the reference cases and only focus on R 4.0 for testing.

[TimTaylor]

Most of these should now have intermediate fixes in #25. I've not been able to get vdiffr working on my local machine so have not checked if image tests are affected by R 4.0.