patch 8.2.1432: various inconsistencies in test files

Problem:    Various inconsistencies in test files.
Solution:   Add modelines where they were missing.  Use Check commands instead
            of silently skipping over tests.  Adjust indents and comments.
            (Ken Takata, closes #6695)
diff --git a/src/testdir/test_sound.vim b/src/testdir/test_sound.vim
index 86dc596..1a9ffb5 100644
--- a/src/testdir/test_sound.vim
+++ b/src/testdir/test_sound.vim
@@ -62,3 +62,5 @@
   sleep 30m
   call assert_true(g:id_again > 0)
 endfunc
+
+" vim: shiftwidth=2 sts=2 expandtab