Testing

Misc

• If the code is for a specific dataset/pipeline, then assertive testing makes more sense than traditional software testing.
• If the code is general purpose, it should be in a package undergo traditional software testing
• Also see
  • Package Development >> Testing
• Packages
  • {assertthat}
  • {testthat}
  • {{pytest}} - It scales down, being super easy to use, but scales up, with mighty features and a rich ecosystem of plugins.
    • Doesn’t add the entry point directory to sys.path. However, you can force it to do so with configuration. (See Make your Python life easier by learning how imports find things about entry points)
  • {{tox}} and {{nox}} - Useful to run tests on different versions of Python to be sure it works with all of them. Both are good but nox is recommended

Assertive Testing

• Testing that happens within the function

• Check for NAs in column

  if (anyNA(dataset$body_mass_g)) {
    rlang::abort("NAs are present in 'body_mass_g' column")
  }

• Assert that I have not inadvertently changed the length of the output dataset either by accidentally dropping rows or accidentally introducing duplicates

  library(testthat)
  make_my_rectangle <- function(dataset_a, dataset_b, dataset_c) {
  
    ... Do stuff
  
    expect_equal(nrow(output_dataset), nrow(dataset_a))
    expect_false(any(duplicated(output_dataset$id)))
  
    output_dataset
  }

• Error functions

  • Too much error code within a function reduces readability. Using functions reduces the lines of code and is reusable.

  • Tidyverse recommends using cli::abort

    • Makes it easy to generate bulleted lists.
    • Uses glue style interpolation to insert data into the error.
    • Supports a wide range of inline markup.
    • Provides convenient tools to chain errors together.
    • Can control the name of the function shown in the error.

  • Example: From link

    check_if_squarable <- function(x,
                                   arg = rlang::caller_arg(x),
                                   call = rlang::caller_env()) {
      x_len <- length(x)
      dims <- sqrt(x_len)
    
      squarable_length <- floor(dims) == dims
    
      if (!squarable_length) {
        cli::cli_abort(
          message = c(
            "Provided vector is not of a squarable length",
            "{.arg {arg}} is of length {.num {x_len}}",
            "This cannot be represented as a perfect square"
          ),
          call = call
        )
      }
    }
    
    check_if_not_numeric <- function(x,
                                     arg = rlang::caller_arg(x),
                                     call = rlang::caller_env()) {
      if (!is.numeric(x)) {
        cli::cli_abort(
          message = c(
            "Provided vector, {.arg {arg}}, must be {.cls numeric}, not {.cls {class(x)}}",
            "We see that {.run is.numeric({.arg {arg}})} returns {.cls {class(x)}}"
          ),
          call = call
        )
      }
    
    }
    
    # Messages
    vector_to_square(data = 1:4)
    #>      [,1] [,2]
    #> [1,]    1    2
    #> [2,]    3    4
    vector_to_square(data = 1:5)
    #> Error in `vector_to_square()`:
    #> ! Provided vector is not of a squarable length
    #> `data` is of length 5
    #> This cannot be represented as a perfect square
    vector_to_square(data = LETTERS[1:4])
    #> Error in `vector_to_square()`:
    #> ! Provided vector, `data`, must be <numeric>, not <character>
    #> We see that `` is.numeric(`data`) `` returns <character>

    • Adding rlang::call_env makes it so when the error is tripped, the error message refers to the function and not the error function.
    • Adding rlang::call_arg makes it so when the error is tripped, the error message states the function’s argument and not “x”