remove uses of testthat::with_mock() (fixes #223)

[jameslamb]

Fixes #223

This removes the one use of testthat::with_mock() in the package, for the reasons mentioned in #223.

It does this by moving the {httr} calls we want to mock into separate internal functions within {uptasticsearch}. Those thin wrappers are introduced here mainly because of the advice from https://testthat.r-lib.org/reference/local_mocked_bindings.html#namespaced-calls

It's trickier to mock functions in other packages that you call with ::. For example, take this minor variation:

some_function <- function() {
  anotherpackage::another_function()
}

To mock this function, you'd need to modify another_function() inside the anotherpackage package. You can do this by supplying the .package argument to local_mocked_bindings() but we don't recommend it because it will affect all calls to anotherpackage::another_function(), not just the calls originating in your package. Instead, it's safer to either import the function into your package, or make a wrapper that you can mock.

Notes for Reviewers

These new internal functions are used in multiple files, so I wanted to centralize them in one other file. Introducing: helperfuns.R 😊

[austin3dickey]

makes sense to me!

[jameslamb]

Thanks! This is the only change we *need to be protected on CRAN ahead of R 4.5.0.

I expect that to come out in April (as every previous minor release has), so we have a bit more time. I'm going to continue with a few other things to try to reduce the we-get-a-fix-or-be-archived-email-from-CRAN risk.

Like these:

• [docs] switch vignettes from 'rmarkdown' to 'markdown' #228
• Drop {httr} dependency #229
• Drop {uuid} dependency #238