[R-pkg-devel] Testing for a Specific R Error

Duncan Murdoch murdoch.duncan at gmail.com
Sat Dec 2 15:43:13 CET 2017

On 02/12/2017 9:23 AM, Dirk Eddelbuettel wrote:
> On 2 December 2017 at 08:38, Bill Denney wrote:
> | Hi,
> |
> | I got a message last night that some of the tests in the PKNCA package do not follow best practices.  ("Do not test the exact format of R messages (from R itself or from other packages): They change, and they can be translated.")  Specifically, I test to ensure that an error is generated when a class cannot be coerced into a data.frame: https://cran.r-project.org/web/checks/check_results_PKNCA.html
> |
> | I want to ensure that I'm getting an error that the variable cannot be coerced into a data.frame.
> |
> | What is the best practice to ensure that I'm getting a specific R error (about coercion) without testing the formatting of the error text?
> To me this suggest testing the _condition_ triggering the error message, as
> opposed to testing for the displayed text of the error message.

Isn't that what Bill suggested in the line below?

 > | The only solution that immediately occurs to me is to wrap the 
coercion in a tryCatch and give my own error.  But, then were the R 
error translated, the users of my package would lose the benefit of 

R does have a system for giving language-independent information about 
errors and warnings:  see the ?signalCondition help page. 
Unfortunately, support for this at the C level is missing, so base 
functions generally don't use it.  You only get something of class 
c("simpleError", "error", "condition").

I don't think there's anything better than Bill's solution, though I 
imagine it is possible to ask for translation of the message.  For 
example, sqrt(-1) currently gives a warning with English message "NaNs 

I can ask to translate that into the current session language using

gettext("NaNs produced", domain = "R")

Figuring out the right thing for "domain" is likely a little painful: 
it depends on which package produced the message, and how.

I don't know if CRAN tests would complain if you tested for equality 
between a warning message and the result of gettext():  it's still true 
that if the English warning changed, the test would fail.

Duncan Murdoch

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