test() should get an options= argument to transparently & temporarily set options for a test #5842

Now, we set options sporadically in the text, e.g.

Having the option set 50, 100, or more lines away from where the value is needed harms readability. It's much better to set the options transparently in the call to test().

Proposed API:

test(..., options = list(key1 = "val1", ..., keyn = "valn"))

# impl
test <- function(..., options = NULL) {
  if (!is.null(options)) {
    old <- do.call("options", options)
    on.exit(options(old), add = TRUE)
  }
  ...
}

Possibly tmp_options= is a better name so as not to clash with options(), then we can do do.call(options, tmp_options).