Re-enter the mocking game

[hadley]

No description provided.

[gaborcsardi]

Cool!

[lionel-]

incorporating what we've learned from mockr and mockery

So what did we learn? I'm curious as I have never used these packages.

[hadley]

What we learned:

• We now have the knowledge and tools to radically simplify the implementation. Compare with_mocked_bindings() to with_mock().
• Now that I've more carefully inspected the implementation of mockery and mockr, I think it actually uses a new technique, and this now seems like "obvious" technique for it to use.
• It's really important for the mocking tool to work in both batch test mode and interactively.

[hadley]

Note that this doesn't appear to work to mock S3 methods.

# In package
mockable_generic <- function(x) {
  UseMethod("mockable_generic")
}
#' @export
mockable_generic.integer <- function(x) {
  x + 1
}

# In test

test_that("local_mocked_bindings affects S3 methods", {
  local_mocked_bindings(mockable_generic.integer = function(x) 100)
  expect_equal(mockable_generic(1L), 100)
})

I tried also binding in the S3 methods table:

  method_env <- ns_env[[".__S3MethodsTable__."]]
  methods <- names(bindings) %in% names(method_env)
  local_bindings(!!!bindings[methods], .env = method_env, .frame = .env)
  bindings <- bindings[!methods]

But while that works when called interactively, it doesn't work in tests.

[lionel-]

For S3 methods it is usually sufficient to bind them in the global environment.

Edit: Though the S3 table might have precedence if existing methods are registered.

[hadley]

@lionel- yeah, that only works for new methods, I think.

But maybe my attempt didn't work because of something to do with the way that testthat sets up environments. It certainly looks like pkgload modifies the same place when unloading packages: https://github.com/r-lib/pkgload/blob/main/R/unload.R#L157-L164. (However, that does suggest that, in general, I need to look in the namespace of the generic, not just the namespace of the current package.)

[hadley]

Oooooh, I wonder if it's because test_env() does env_clone(asNamespace(package)).