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The goal of mockr is to provide a drop-in replacement for testthat::with_mock() which will be deprecated in the next version of testthat. The only exported function, with_mock(), is modeled closely after the original implementation, but now only allows mocking functions in the package under test. In contrast to the original implementation, no fiddling with R's internals is needed, and the implementation plays well with byte-compiled code. There are some caveats, though:

  1. Mocking external functions (in other packages) doesn't work anymore. This is by design.
  2. You cannot refer to functions in your package via your.package:: or your.package::: anymore, this is a limitation of the implementation.

If you encounter other problems, please file an issue.


some_func <- function() stop("oops")
some_other_func <- function() some_func()

# Calling this function gives an error
#> Error in some_func(): oops

tester_func <- function() {
  # Here, we override the function that raises the error
    some_func = function() 42,

# No error raised
#> [1] 42

# Mocking doesn't override functions in the same environment by design
with_mock(some_func = function() 6 * 7, some_other_func())
#> Error in some_func(): oops


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