Check if a function is called inside another function

Question

Let say I have the function

mean_wrapper <- function(x) {
  mean(x)
}

How can I check if the mean function is called?

An use case is for instance If I want to check this behavior in a unit test.

EDIT:

I make another exampe to be clearer. Let consider this function:

library(readr)
library(magrittr)

read_data <- function(file_name) {
  read_csv(file_name) %>%
    validate_data()
}

The aim of read_data is to read a CVS file and validate it. validate_data performs some checks on the data. It raises an error if one of them fail, otherwise returns the input object.

I want to test both functions but I don't want replicate the same tests I wrote for validate_data in the case of read_data. Anyway I have to check that the latter function has been called in read_data, so I wolud like to write a test that does this for me.

Check this tutorial to maybe get you started thinking about unit testing in R. There is a package called RUnit for unit testing. — Tim Biegeleisen
– Tim Biegeleisen, Commented Aug 21, 2017 at 13:56
Actually I need a strategy to check the call in a unit test, in general I know how to perform unit test :) — amarchin
– amarchin, Commented Aug 21, 2017 at 13:59
I'm not sure if I understand what you need. Can you explain in more detail? Maybe crawl the expression tree returned by body(mean_wrapper) for an expression of more than two elements with mean as the first element? — Roland
– Roland, Commented Aug 21, 2017 at 14:12
I'll edit the question so that what I am asking should be clearer — amarchin
– amarchin, Commented Aug 21, 2017 at 14:29

Roland · Accepted Answer · 2017-08-21 14:16:05Z

2

You could trace mean:

trace(mean, tracer = quote(message("mean was called")))
mean_wrapper(3)
#Tracing mean(x) on entry 
#mean was called
#[1] 3
untrace(mean)
#Untracing function "mean" in package "base"

Instead of a message you can use anything (e.g., assignment to a variable in the enclosing environment) as tracer.

answered Aug 21, 2017 at 14:16

Roland

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2 Comments

amarchin Over a year ago

That's an interesting approach, I am checking if it works for me.

amarchin Over a year ago

The approach works when I use devtools::test() but it doesn't when I use devtools::check(document = FALSE) or in the CI environment.

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