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?

Answer 1

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.