R tests using deprecated testthat functionality

[jameslamb]

{testthat} 3.0.0 was released in October 2020, and some functionality {uptasticsearch} uses from it is now considered deprecated.

From the {testthat} vignettes on v3.x (link), the following are deprecated and may be removed in a future major release:

• testthat::context()
• testthat::with_mock()

Uses of these functions should be removed, to prevent the package being removed from CRAN in the future if / when {testthat} completely removes those functions.

[jameslamb]

I didn't realize we already had this issue 🤦🏻

context() was removed in #232

with_mock() was removed in #237 (linking #223 )

This is now complete.