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Simple assertions with sensible defaults and customisable error messages.


The goals with assertions are to provide

  1. Convenient assertion calls (e.g. assert_number())

  2. A general assert function that asserts any possible condition/s and throws informative error messages

  3. Extremely user friendly error message defaults.

  4. Easily customisable error messages, with inline code evaluation & styling powered by the cli package

  5. Simple creation of custom assertion functions with user-specified defaults



Development version

To get a bug fix or to use a feature from the development version, you can install the development version of assertions from GitHub.

# install.packages('remotes')

Quick Start

All assertions start with assert, which means you just type it in and levarage autocomplete suggestions to look through all available options

# Load library

# Use premade assertions
assert_character(c('a', 'b', 'c'))

# Assert anything 
assert(1000 % 2 == 0)

# Assert multiple conditions at once (all must be true)
assert(1000 % 2 == 0, 6/2 == 3)

Customizing Error Messages

# Customise any error messages using the `msg` argument
assert_number("A", msg = "Please supply a number!")

# Evaluate code in your error message using '{}' operators
foo = "A"
assert_number(foo, msg = "'{foo}' is not a number :(. Try again")

# Emphasise cetain words in error using {.strong text_to_emphasise}
assert_number("A", msg = "{.strong Try again}")

For advanced customisation, see cli documentation

Create your own assertion functions

Have a custom assertion you want to use repeatedly?

Creating your own assertion functions is extremely easy

Just use assert_create(), you just need to supply:

  1. a function that returns TRUE/FALSE when assertion should PASS/FAIL

  2. a default error message

How about an example?

# Create a function that asserts input is lowercase 
assert_lowercase <- assert_create(
  func = function(x) {x == tolower(x)}, 
  default_error_msg = "'{arg_name}' must be entirely lowercase" 

#Assertion passes if input is lowercase
assert_lowercase("all lower case")

#But throws the expected error if uppercase characters are present
assert_lowercase("NOT all lower case") 

See ?assert_create() for details

Vectorised assertions

Assertions may have vectorised versions that test whether all elements in a vector/matrix meet a condition.

For example:

Vectorised functions have the assert_all_ prefix.

Contributing to this package

Two options

Request an assertion

  1. Open a github issue and request away. I’m happy to implement a tonne more assertions, just let me know what you want

Creating assertions yourself

  1. Create a custom assert_something function with a call to assert_create() or assert_create_chain()

  2. Create a github issue with the assertion creation code + any helper function you pass to the func argument (e.g. is_something())

Similar Packages

Great alternative packages for writing assertions include:

Each package has its own features and syntax. So hopefully there is one that suits your needs and preferences. I’m a big fan of checkmate for its speed, assertive for its huge library of ready-made assertion functions, and assertthat for its error message customization.