with_mock
Mock functions in a package.
Description
![[Superseded]](../help/figures/lifecycle-superseded.svg)
Mocking allows you to temporary replace the implementation of functions within a package, which useful for testing code that relies on functions that are slow, have unintended side effects or access resources that may not be available when testing.
This works by using some C code to temporarily modify the mocked function in place. On exit, all functions are restored to their previous state. This is somewhat abusive of R's internals so use with care. In particular, functions in base packages cannot be mocked; to work aroud you'll need to make a wrapper function in your own package..
Usage
with_mock(..., .env = topenv()) local_mock(..., .env = topenv(), .local_envir = parent.frame())
Arguments
... |
named parameters redefine mocked functions, unnamed parameters will be evaluated after mocking the functions |
.env |
the environment in which to patch the functions, defaults to the top-level environment. A character is interpreted as package name. |
.local_env |
Environment in which to add exit hander. For expert use only. |
Value
The result of the last unnamed parameter
3rd edition
![[Deprecated]](../help/figures/lifecycle-deprecated.svg)
with_mock() and local_mock() are deprecated in the third edition.
References
Suraj Gupta (2012): How R Searches And Finds Stuff
Examples
add_one <- function(x) x + 1
expect_equal(add_one(2), 3)
with_mock(
add_one = function(x) x - 1,
expect_equal(add_one(2), 1)
)
square_add_one <- function(x) add_one(x)^2
expect_equal(square_add_one(2), 9)
expect_equal(
with_mock(
add_one = function(x) x - 1,
square_add_one(2)
),
1
)
# local_mock() -------------------------------
plus <- function(x, y) x + y
test_that("plus(1, 1) == 2", {
expect_equal(plus(1, 1), 2)
})
test_that("plus(1, 1) == 3", {
local_mock(plus = function(x, y) 3)
expect_equal(plus(1, 1), 3)
})