testthat fails, yet same code works in a standard test

[hofnerb]

In my package papeR I have the following lines in my code

## overwrite standard generic
labels <- function(object, ...)
    UseMethod("labels")

## per default fall back to standard generic
labels.default <- function(object, ...)
    UseMethod("base::labels")

If I am using

labels(matrix(1:10))

in a standard file in tests, e.g. in tests/regtest-prettify.R everything works as expected and I get

## [[1]]
## [1] "1"  "2"  "3"  "4"  "5"  "6"  "7"  "8"  "9"  "10"
## 
## [[2]]
## [1] "1"

The same is true if I run the code after installing the package.

Yet, if I put this code in tests/testthat/test-labels.R, I get (essentially) the following error

no applicable method for 'base::labels' applied to an object of class "c('matrix', 'integer', 'numeric')"

Now, I wonder
a) why this happens
b) why this happens only with testthat
c) how I can debug and solve this.

[kevinushey]

This fails directly for me (ie, is not a testthat issue):

## overwrite standard generic
labels <- function(object, ...)
    UseMethod("labels")

## per default fall back to standard generic
labels.default <- function(object, ...)
    UseMethod("base::labels")

labels(matrix(1:10))

Either way, do you really want to override the generic? Can't you just implement a labels method for your own class?

[hofnerb]

That's true. But

install_github("hofnerb/papeR")
library("papeR")
labels
labels(matrix(1:10))

does work, though.

In essence I currently do not need to overwrite the standard generic. However, I wanted to add a special behaviour such that I can extract variable labels by

df <- data.frame(x = 1:3, y  = 4:6)
df <- as.ldf(df)
labels(df$x)

which should return

attr(df$x, "variable.label")

I was thinking of something along the lines of

labels.default <- function(object, ...) {
    if (!is.null(attr(object, "variable.label"))) {
        return(attr(object, "variable.label"))
    }
    UseMethod("base::labels")
}

which wouldn't change standard behaviour per se. [We had this discussion already elsewhere btw].

---

However, I was just thinking to also give a new (additional) class to all "columns" of the data frame to allow method dispatch to work.

Still, I am puzzled why this happens that way.

[hadley]

I think you want base::labels(object, ...), not UseMethod("base::labels"). But I agree with @kevinushey that override a generic is a bad idea.