-This directory contains metainformation about the gnulib modules, one file
-per module. These files are used by gnulib-tool.
+This directory contains metainformation about the gnulib modules, one or two
+files per module. These files are used by gnulib-tool.
+
+For every module,
+ - the file <module> is the metainformation about the library code of the
+ module,
+ - the file <module>-tests is the metainformation about the unit test of
+ the module (optional but recommended).