[pytest-dev] Displaying additional test failure information

[Jurko Gospodnetić]

   Hi all.

   I was wondering if anyone can tell me the cleanest way to make 
assertions in a specific part of my test code (e.g. a specific test 
class or module) report some extra information on test failure?

   I can add a regular assertion description string, and that displays 
the extra information but it also avoids regular pytest test failure 
result reporting which I would like to keep.

   I can also print out the extra information directly to stdout/stderr 
- but that can be hard to read, especially if the test prints out other 
data as well.

Usage scenario:
---------------
   Imagine a class for comparing two XML structures. That class 
maintains some context information that would be useful to print out 
when an XML mismatch is detected. For example, if it detects two nodes 
with different namespaces, you want it to:
   - report exactly which nodes these are and not just 'there exist two 
nodes with mismatched namespaces'
   - make this information available without the developer having to 
drop into the debugger

   If possible, it would also be a great plus if this extra content 
could be integrated into the regular 'red' assertion failure information.

   Best regards,
     Jurko Gospodnetić