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

On Thu, 16 Jul 2020, Ben Bolker wrote:

FWIW/in defense of the OP, this is a *very* common idiom in the base R

code

base.  There may be some false positives, but

 find . -name "*.Rd" -exec grep -Fl "stopifnot(" {} \; | grep -v doc | wc

lists 187 files, e.g. from src/library/utils/man/object.size.Rd

And I probably wrote some of them, but I don't think I would now.
As a rule, I think the documentation is clearer without the tests.

On the other hand, we don't all agree on these things.

stopifnot(identical( ## assert that all three are the same :
             unique(substr(as.vector(fsl), 1,5)),
             format(round(as.vector(sl)/1024, 1))))


On 7/16/20 2:02 PM, luke-tierney at uiowa.edu wrote:

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

--
Luke Tierney
Ralph E. Wareham Professor of Mathematical Sciences
University of Iowa                  Phone:             319-335-3386
Department of Statistics and        Fax:               319-335-3017
    Actuarial Science
241 Schaeffer Hall                  email:   luke-tierney at uiowa.edu
Iowa City, IA 52242                 WWW:  http://www.stat.uiowa.edu