internal: replace mockery functions in package tests with testthat::with_mocked_bindings()

[francisbarton]

with_mocked_bindings() and local_mocked_bindings() provide tools for "mocking", temporarily redefining a function so that it behaves differently during tests. This is helpful for testing functions that depend on external state (i.e. reading a value from a file or a website, or pretending a package is or isn't installed).

These functions represent a second attempt at bringing mocking to testthat, incorporating what we've learned from the mockr, mockery, and mockthat packages.

https://testthat.r-lib.org/reference/local_mocked_bindings.html

This package is superseded and we no longer recommend that you use it for new tests. We instead recommend testthat::local_mocked_bindings().

https://github.com/r-lib/mockery

[francisbarton]

Sorry, not sure this is a priority!