Exploring expect statements

Developing R Packages

Jasmin Ludolf

Content Developer

Most common expect statements

In testthat package:

expect_error(): error from object call
- Errors stop code execution; warnings don't
expect_warning(): warning produced by object call

#' @examples
#' # Convert 32F to C
#' temp_converter(32, "Fahrenheit", "Celsius")

[1] 0

In the tests/testthat/test-temp_converter.R file:

library(testthat)
expect_equal(

  object = temp_converter(32, "Fahrenheit", "Celsius"),

  expected = 0

)

expect_identical(sqrt(3) ^ 2, 3)

Error: sqrt(3)^2 (`actual`) not 
identical to 3 (`expected`).

  `actual`: 2.9999999999999996
`expected`: 3.0000000000000000

expect_equal(sqrt(3) ^ 2, 3)

expect_equal()
- Allows for small differences
- Has a tolerance argument, default usually good

expect_output(

    print("Testing R Packages is fun"),

   "funk"

)

Error: `print\("Testing R Packages is 
fun"\)` does not match "funk".
Actual value: "\[1\] "Testing R 
Packages is fun""

Output diagram

expect_warning(
  temp_converter(-40, 
                 "Celsius", 
                 "Celsius")
)

Warning sign

expect_error(
  temp_converter(300, 
                 "Kelvin", 
                 "Fahrenheit")
)

Error sign

Each expectation should test an aspect of a function
When combined together, 100% of function aspects should be covered by unit tests

Developing R Packages