Include line diff in numdiff output

[class4kayaker]

When running tests, if Numdiff is used only the differing values and their position in the lines in question are shown in the generated diff files. This results in having to either visually do the comparison, use another diff tool or redoing the diff using "numdiff -V" in order to obtain the context of the variations between the two. The change made is to use "numdiff -V" when generating the DIFF_OUTPUT intended to become *.diff or *.diff.failed in order to also include the originating lines when printing the diff.

Is not making use of this flag an intended design decision, a compatibility limitation, or was the capability overlooked?

[bangerth]

That's one way. I thought I used a different approach in ASPECT, where my idea was to show both the output of numdiff and if there is a difference, also the output of diff for context. But I can't seem to find that code right now. Let's just try it with your code and see if we like it!

[bangerth]

/run-tests

[class4kayaker]

If you would prefer the approach of numdiff output followed by diff output if a difference exists, I believe I could modify the current approach to correctly do this. I checked deal.II, and that is the method that it uses, so I could start trying to model the diff script on that. It might still be desirable to use the "-V" flag as it will print the lines which vary above the changed values, so it would be possible to view the immediate context with the numerical diff rather than a line number and position. I can currently do tests against the matrix_nonzeros test and a few others I know I have locally varying behavior for, and give samples of the output.

[bangerth]

Ah, yes, I did that in deal.II apparently.

Not to worry. Let's just try what we get here and if we don't like it, we can always change it again.