local_test_context() and local_reproducible_output()
set the following options with withr::local_options():
cli.unicode (default: FALSE) so that the cli package never generates unicode
output (normally cli uses unicode on Linux/Mac but not Windows).
Windows can't easily save unicode output to disk, so it must be set to
false for consistency.
crayon.enabled (default: FALSE) suppresses ANSI colours generated by the crayon
package (normally colours are used if crayon detects that you're in a
terminal that supports colour).
width (default: 80) to control the width of printed output (usually this
varies with the size of your console).
In addition, local_test_context() sets the following options:
cli.dynamic = FALSE so that tests assume that they are not run in
a dynamic console (i.e. one where you can move the cursor around).
lifecycle_verbosity = "warning" so that every lifecycle problem always
generates a warning (otherwise deprecated functions don't generate a
warning every time).
OutDec = "." so numbers always uses . as the decimal point
(European users sometimes set OutDec = ",".)
rlang_interactive = FALSE so that rlang::is_interactive() returns
FALSE, and code that uses it assumes you're in a non-interactive
environment.
useFancyQuotes = FALSE so base R functions always use regular (straight)
quotes (otherwise the default is locale dependent, see sQuote() for
details).
local_test_context() also sets envvars RSTUDIO = 0 (which ensures that RStudio is never
detected as running), and TESTTHAT = "true" (which ensures that
is_testing() returns TRUE), and sets collation locale to "C"
(which ensures that character sorting the same regardless of current
locale).