CG: add information about Regtest Checking Project (issue 5669047)

[janek . lilypond]

Reviewers: ,

Message:
Please review.
The most important question is: will this be clear for average user, who
hadn't participated in development previously?

Description:
CG: add information about Regtest Checking Project

Phil Holmes wrote a nice web app that allows people to
review regtests, one at a time.  We can ask users for
help and thus painlessly do a full regtest check.
This commit contains brief instructions how to use the app.

Please review this at http://codereview.appspot.com/5669047/

Affected files:
  M Documentation/contributor/regressions.itexi


Index: Documentation/contributor/regressions.itexi
diff --git a/Documentation/contributor/regressions.itexi  
b/Documentation/contributor/regressions.itexi
index  
b23e6b1abb99c7e2c7f2ec355c498c938aff9576..1c59fcbe5c7f36a85f612e01227c22eeb696d0c0  
100644
--- a/Documentation/contributor/regressions.itexi
+++ b/Documentation/contributor/regressions.itexi
@@ -470,3 +470,45 @@ available in the LilyPond documentation:
  
@uref{http://lilypond.org/doc/latest/input/regression/musicxml/collated-files}
 @end example

+
address@hidden Grand Regression Test Checking
address@hidden Grand Regression Test Checking
+
address@hidden What is this all about?
+
+Regression tests (usually abbreviated "regtests") is a collection
+of @file{.ly} files used to check whether LilyPond is working correctly.
+Example: before version 2.15.12 breve noteheads had incorrect width,
+which resulted in collisions with other objects.  After the issue was  
fixed,
+a small @file{.ly} file demonstrating the problem was added to the  
regression
+tests as a proof that the fix works.  If someone will accidentally break
+breve width again, we will notice this in the output of that regression  
test.
+
+We are asking you to help us by checking a regtest or two from time to  
time.
+You don't need programming skills to do this, not even LilyPond skills -
+just basic music notation knowledge; checking one regtest takes less than
+a minute.  Simply go here:
+
address@hidden
address@hidden://www.holmessoft.co.uk/homepage/private/regtests/}
address@hidden example
+
address@hidden Some tips on checking regtests
+
address@hidden Description text
+
+The description should be clear even for a music beginner.
+If there are any special terms used in the description,
+they all should be explained in our
address@hidden Glossary,music-glossary,@manualDevelGlossarySplit}
+or @docLinkBig{Internals Reference,internals,@manualDevelInternalsBig}.
+Vague descriptions (like "behaves well", "looks reasonable") shouldn't be  
used.
+
address@hidden Regtest "design"
+
+Unfortunately some regtests are written poorly.  A good regtest should be
+straightforward: it should be obvious what it checks and how.  Also,
+it shouldn't check everything at once.  For example it's a bad idea to test
+accidental placement by constucting one huge chord with many suspended  
notes
+and loads of accidentals.  Rather,   cases should be tested, and they  
should be
+clearly separated.