Testing private methods in R6 classes in R

Question

I am currently using R6 classes in a project.

I would like to write unit tests that also test the functionality of private methods that I am using (preferably by not going through the more complicated public methods that are using these private methods).

However, I can't access seem to access the private methods.

How do I best do that?

Thanks!

Answer 1

Here is a solution that does not require environment hacking or altering the class you want to test, but instead creating a new class that does the testing for you.

In R6, derived classes have access to private Methods of their base classes (unlike in C++ or Java where you need the protected keyword to archieve the same result). Therefore, you can write a TesterClass that derives from the class you want to test. For example:

ClassToTest <- R6::R6Class(
  private = list(
    privateMember = 7,
    privateFunction = function(x) {
      return(x * private$privateMember)
    }
  )
)

TesterClass <- R6::R6Class(
  inherit = ClassToTest,
  public = list(
    runTest = function(x = 5) {
      if (x * private$privateMember != private$privateFunction(x))
        cat("Oops. Somethig is wrong\n")
      else
        cat("Everything is fine\n")
    }
  )
)

t <- TesterClass$new()
t$runTest()
#> Everything is fine

One advantage of this approach is that you can save detailed test results in the TesterClass.