Doc : update CG "Regression tests"

This commit updates the first, basic section about
regtest compilation.  It may need to be completed.

diff --git a/Documentation/contributor/regressions.itexi b/Documentation/contributor/regressions.itexi
index 5c32f97e15745959617e9c5aa394e038e8fcad10..e8df94609d5f05f7e471b8aa6051bd85f4b407f5 100644 (file)
--- a/Documentation/contributor/regressions.itexi
+++ b/Documentation/contributor/regressions.itexi
@@ -36,6 +36,50 @@ of different versions to see when bugs appeared.
 @section Current regtest output
 
 
+@TODO: To be checked and completed -vv
+
+The easiest way to see the @q{current} regtest output (meaning,
+the ouput of the latest stable or development version) is
+to look at the precompiled regtest
+@uref{../../input/regression/collated-files.html, HTML page} or its
+@uref{../../input/regression/collated-files.pdf, pdf version}.
+
+However, depending on how many changes have been made to the code
+since the latest release, this page may not reflect the latest
+features, bugfixes... or new bugs that may have been introduced!
+
+Therefore, if you have an appropriate environment to build LilyPond
+yourself, it is recommended that you compile the software yourself.
+
+The first step is to download the latest available source code,
+as explained in @ref{Working with source code}.  Then you will need
+to build the LilyPond binary@footnote{Uninstalling the previous
+LilyPond version is not necessary, nor is running @code{make install},
+since the tests will automatically be compiled with the LilyPond binary
+you have just built in your source directory.}: see
+@rcontrib{Compiling LilyPond}.
+
+From this point, compiling the regtests is as simple as running
+
+@example
+  make test
+@end example
+
+However, as there are many snippets to compile, if you have a multi-core
+machine it is highly recommended to use the @option{-j} option, as
+described in @ref{Saving time with the @option{-j} option}.  Another
+useful optimization is to set the @var{CPU_COUNT} variable; for a
+quad-core processor the complete command would look like
+
+@example
+  make -j5 CPU_COUNT=4 test
+@end example
+
+The regtest output will then be available in one of the
+@file{input/regression/out-*} directories, depending on the
+exact command you used.
+
+
 @node Comparison regtest output
 @section Comparison regtest output