CRAN Debian File Handling Differences?

[David Blodgett]

Dear R Package Development Community,

I'm working on some CRAN Debian test failures (https://win-builder.r-project.org/incoming_pretest/ncdfgeom_1.0.0_20190423_031452/). The tests all pass on rhub Debian, CRAN windows, local OSX, and Travis Ubuntu. The tests that are failing on CRAN Debian are ones where I check that changes got made to an existing file that is modified in place by my package code. 

Are there nuances of the CRAN environment that prevent a `tempfile()` file being created then modified at run time? What is a suggested best practice for such a test? 

I may just disable this set of tests on CRAN for the time being since it passes on so many environments, but want to do my due diligence and decrease fragility as much as possible.

Thanks for any guidance you can offer. 

Regards,

- Dave