Follow the standard when the count is set to zero. Or let me say it differently,

follow the statement from the standard that make the most sense to me. In this
particular case this statement is:
If there is no active handle in the list it returns outcount = MPI_UNDEFINED.

This commit was SVN r9512.

NEWS

@@ -23,6 +23,7 @@ version 1.0.
 1.1
 ---
 
+- Open MPI accept a count = 0 in all multiple completion MPI functions.
 - The PERUSE support is now available directly on the trunk. In order to
   activate it add --enable-peruse to the configure options. All events
   described in the PERUSE 2.0 draft are supported, plus one Open MPI

ompi/mpi/c/testsome.c

@@ -61,8 +61,12 @@ int MPI_Testsome(int incount, MPI_Request requests[],
     /* optimize this in the future */
     rc = ompi_request_test_any(incount, requests, &index, &completed, pstatus);
     if(completed) {
-        *outcount = (index == MPI_UNDEFINED) ? MPI_UNDEFINED : 1;
-        indices[0] = index;
+        if( MPI_UNDEFINED == index ) {
+            *outcount = MPI_UNDEFINED;
+        } else {
+            *outcount = 1;
+            indices[0] = index;
+        }
     } else {
         *outcount = 0;
     }