Use canned data in vignettes

[florianm]

Problem

Karissa found:

• Installation succeeds as documented.
• remotes::install_github() works by default, but fails when build_vignettes = TRUE if you do not have your credentials stored prior to build.

Jason found same breakage with auth credentials not available in devtools::install(build_vignettes=TRUE).

Solution

• Have a squizzle at https://github.com/ropensci/rcites/blob/master/vignettes/a_get_started.Rmd for best practices: Vignettes decide whether or not to eval code chunks based on an environment variable (in this case NOT_CRAN) and both ways are tested in the Travis-CI testing grid. https://github.com/ropensci/rcites/blob/master/.travis.yml
• Include canned data for all results from all web requests sent by vignettes.
• This will enable vignettes to build from canned data without the need for ODK Central sandbox credentials.
• This will require extra tests to verify that canned data is identical to results from web requests.
• Add a clear delineation as to what can be done with and without test credentials.

source ropensci/software-review#335 (comment)