[PATCH] Document do_test in test-skeleton.c

[Steve Ellcey <sellcey@cavium.com>]

While working on a patch for math/test-tgmath2.c I learned some information
about do_test and how it should work.  Here is my attempt to put that 
information into test-skeleton.c.  If it looks accurate I could put this
information in the GLIBC Wiki too, in the "Writing a test case" section.
The comments about writing to stdout instead of stderr is already in the Wiki,
but the return value descriptions are not.

Steve Ellcey
sellcey@caviumnetworks.com



2016-11-04  Steve Ellcey  <sellcey@caviumnetworks.com>

	* test-skeleton.c: Document do_test usage.


diff --git a/test-skeleton.c b/test-skeleton.c
index 55841fb..cbd0c2d 100644
--- a/test-skeleton.c
+++ b/test-skeleton.c
@@ -36,7 +36,22 @@
 
 /* The test function is normally called `do_test' and it is called
    with argc and argv as the arguments.  We nevertheless provide the
-   possibility to overwrite this name.  */
+   possibility to overwrite this name.
+
+   The test function should have a return type of 'int' and should
+   return 0 to indicate a passing test, 1 to indicate a failing test,
+   or 77 to indicate an unsupported test.  Other result values could be
+   used to indicate a failing test but since the result of the test
+   function is passed to exit and exit only returns the lower 8 bits of
+   its input a non-zero return with some values could cause a test to
+   incorrectly be considered passing when it really failed. For this
+   reason tests should always return 0, 1, or 77.
+
+   The test function may print out diagnostic or warning messages as well
+   as messages about failures.  These messages should be printed to stdout
+   and not stderr so that the output is properly ordered with respect to
+   the rest of the glibc testsuite run output.  */
+
 #ifndef TEST_FUNCTION
 # define TEST_FUNCTION do_test (argc, argv)
 #endif