Doc: CG: Add introduction to regression tests

diff --git a/Documentation/contributor/regressions.itexi b/Documentation/contributor/regressions.itexi
index f5cf54c11295836e11c7e4e1848a82d42fb18f92..5c32f97e15745959617e9c5aa394e038e8fcad10 100644 (file)
--- a/Documentation/contributor/regressions.itexi
+++ b/Documentation/contributor/regressions.itexi
@@ -3,16 +3,34 @@
 @chapter Regression tests
 
 @menu
-* Introduction to regression tests::  
-* Current regtest output::      
-* Comparison regtest output::   
-* MusicXML tests::              
+* Introduction to regression tests::
+* Current regtest output::
+* Comparison regtest output::
+* MusicXML tests::
 @end menu
 
 
 @node Introduction to regression tests
 @section Introduction to regression tests
 
+LilyPond has a complete suite of regression tests that are used
+to ensure that changes to the code do not break existing behavior.
+These regression tests comprise small LilyPond snippets that test
+the functionality of each part of LilyPond.
+
+Regression tests are added when new functionality is added to
+LilyPond.  They are also added when bugs are identified.  The
+snippet that causes the bug becomes a regression test to verify
+that the bug has been fixed.
+
+The regression tests are automatically compiled using special @code{make}
+targets.  The output of the regression tests is also automatically
+checked to identify changes in LilyPond output.
+
+The output of the regression tests is available on the website
+for every stable version of LilyPond.  This allows the comparison
+of different versions to see when bugs appeared.
+
 
 @node Current regtest output
 @section Current regtest output