How to check if a substring exists inside a 'Result' object with Robot Framework? - robotframework

Question

I am running the following test inside Robot Framework:
*** Settings ***
Documentation This initializes testrun.robot
Library Process
Library OperatingSystem
Library XML
Library Collections
Output Is A Valid XML File Against JATS format
Start Process xmllint --dtdvalid http://jats.nlm.nih.gov/archiving/1.1d3/JATS-archivearticle1.dtd ./output/nlm/out.xml shell=True
${result}= Wait For Process timeout=45 secs
Log ${result.stdout}
Log ${result.stderr}
Run Keyword Unless '${result.stderr} == ${EMPTY}' Should Contain ${result.stderr} element xref: validity error : IDREFS attribute rid references an unknown
The variable ${result.stderr} is a string that contains the substring 'element xref: validity error : IDREFS attribute rid references an unknown'. As far as I know, I'm not dealing with any whitespace errors or quotation problems, although I could be wrong. (I've been fiddling around with that for a while now.)
Thanks for the help!
Edit: The log that Robot Framework generates tells me that the process has finished (that's how I know what result.stderr contains.)

Answer 1

Consider this statement:
Run Keyword Unless '${result.stderr} == ${EMPTY}' ...
The keyword will never run because you aren't comparing two variables, you are simply checking whether the string literal string '${result.stderr} == ${EMPTY}' is not empty (and it's not, because it has 28 characters).
It is the same as if you did this in python:
if len('${result.stderr} == ${EMPTY}') > 0:
...
You need to put the single quotes around each variable separately so that you are passing a valid expression to the if statement, rather than a string that looks like a valid expression:
Run Keyword Unless '${result.stderr}' == '${EMPTY}' ...