[R-pkg-devel] [External] Re: Interpret feedback: not write testthat-tests in examples

On Thu, 16 Jul 2020, Henrik Bengtsson wrote:

If the point of having, say,

stopifnot(add(1, 2) == sum(c(1, 2))

is to make it explicit to the reader that your add() function gives
the same results as sum(), then I argue that is valid to use in an
example.? I'm pretty sure I've used that in some of my examples.? For
the purpose, there should be no reason why you can't use other
"assert" functions for this purpose, e.g.

testthat::expect_equal(add(1, 2), sum(c(1, 2))

If the point is to communicate this to users I would write something like

## The following evaluates to TRUE:
add(1, 2) == sum(c(1, 2)

Using stopifnot just adds clutter that obscures the message for a
human reader; testthat::expect_equal even more so.

Best,

luke

Now, if the point of your "assert" statement is only to validate your
package/code, then I agree it should not be in the example code
because it adds clutter.? Such validation should be in a package test.

So, if the former, I suggest you reply to the CRAN Team and explain 
this.

/Henrik

On Thu, Jul 16, 2020 at 6:28 AM Richel Bilderbeek
<richel at richelbilderbeek.nl> wrote:

Dear R package developers,

I would enjoy some help regarding some feedback I got on my package 
from a CRAN volunteer, as I am unsure how to interpret this correctly.

This is the feedback I got (I added '[do]'):

Please [do] not write testthat-tests in your examples.

I wonder if this is about using `testthat` or using tests in general.

To simplify the context, say I wrote a package with a function 
called `add`, that adds two numbers. My example code would then be 
something like this:

```
library(testthat)

expect_equal(add(1, 2), 3)
```

The first interpretation is about using `testthat`: maybe I should 
use base R (`stopifnot`) or another testing library (`testit`) or 
hand-craft it myself?

The second interpretation is about using tests in example code. I 
like to actively demonstrate that my code works as expected. I 
checked the policies regarding examples, and I could not find a rule 
that I should refrain from doing so.

What is the correct response to this feedback?

Thanks for your guidance, Richel Bilderbeek