Unit testing in R using testthat library Exercises

March 12, 2017
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(This article was first published on R-exercises, and kindly contributed to R-bloggers)

testthat is a testing framework developed by Hadley Wickham, which makes unit testing easy for developers.

Test scripts developed can be re-run after debugging or making changes to the functions without the hassle of developing the code for testing again.

testthat has a heirarchical structure made up of expectations, tests and contexts.
Visit this link to know more.

You should be familiar with creation of functions in R to know how this testing framework works.

Answers to the exercises are available here.

Exercise 1

Install and load the package testthat using the appropriate function.

Exercise 2

expect_that() is the function that makes the binary assertion of whether or not the value is as expected.
expect_that(x,equals(y)) reads as “it is expected that ‘a’ will be equal to ‘b’”.

Use this function to see if 5*2 equals 10

Learn more about Hadley Wickhams usefull packages in the online course R Data Pre-Processing & Data Management Shape your Data!. In this course you will learn how to work with:

  • tidyr, cleaning your data
  • dplyr, shape your data
  • And much more

Exercise 3

The function equals() checks for equality with a numerical tolerance. Let’s see what that tolerance level is

Use appropriate function to see if 5*2 equals 10 + (1e-7).
Does the test fail?
If no, change the value to 1e-6 and see what happens.

Exercise 4

To exactly match the values is_identical_to() can be used instead of equals()

Using the appropriate function, check if 2*2 is identical to 4 + (1e-8)

Please check the documentation of this package to learn more about the available functions.

Exercise 5

Let us create a function (m) to multiply two numbers ( two arguments ) and check if it throws an error with character input arguments.

Check if m(“2″,”3”) throws an error “non-numeric argument to binary operator”

Exercise 6

Now that we know how to check for expectations, let us create tests.
Test is a collection of expectations, where these expectations test a single item of the functionality of a process.

test_that() is the function that encapsulates the description and the code to test each expectation.

The first argument is the description and the second argument is a collection of expectations.

Create a test for function ‘m’ with description “Testing multiplication function” and add a few scenarios to it.
1. Check if m(2,3) equals 6
2. Check if m(2,c(2,3)) equals c(4,6)
3. Check if m(2,”3″) throws an error “non-numeric argument to binary operator”

Exercise 7

The User can write his own expectation using the expect() function. This expectation should compare the input value and the expectation and report the result.
The syntax to write one is as below.

custom_expectation <- function() {function(x) {expectation(condition, "Failure message")}}

Now, write an expectation is_greater_10() to check if a number is greater than 10

Exercise 8

Use the expectation defined above to check if 9 is greater than 10.

Exercise 9

tests can be put together in a file and run at once. Write tests of your choice and save them in a file.
Use the function test_file() to run all the tests in the file.

Exercise 10

Test files in a directory can be run at once using the function test_dir().
Create multiple test files and save them in a directory. Run all the tests at once using the function.

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