Package checking: verifying plots

I pride myself on having an extensive and comprehensive test suite for the survival package.

However, I don't have a good procedure for testing the plotting routines.  (Forget "good", 
I don't even have a third-rate procedure for this.)  This was brought home with the latest 
release; within 24 hours I got a note about a problem.  They y-axis range for a plot was 
calculated incorrectly, giving no warning or error, just a graph with 2/3 of the data 
outside the plot window.  It was a side effect of a change for another reason, and of 
course I had checked out that consequence thoroughly.

Any good ideas for this issue?

Terry Therneau