Test if a function uses another function

Question

Is there a way to determine if a function calls another function? For example, I would like to know if a user-created function (lets say f()) uses a function (example sum()).

f <- function(x, y) {
  sum(x, y)
}

# test_if_f_uses_sum(f)

^{Created on 2019-06-11 by the reprex package (v0.3.0)}