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

[Robert M. Flight]

Richel,

I think that feedback is important. Examples are examples first, and tests
second, as in if your examples no longer work, then maybe you need to check
your underlying code.

{testthat} tests belong in their own `tests` directory, and are used to
directly test your code and provide feedback about whether your code is
working.

The pattern I normally see if you want to directly check the output of an
example is a `stopifnot(x == y)`, but I've never observed having
`expect_equal` in example code.

There might not be a policy against it, but I think the general expectation
is that {testthat} code stays in `tests`, not in examples in the
documentation.

-Robert

On Thu, Jul 16, 2020 at 9:28 AM Richel Bilderbeek <
richel using 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
>
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