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_shift.vim b/src/testdir/test_shift.vim
index 4ff054f..370082f 100644
--- a/src/testdir/test_shift.vim
+++ b/src/testdir/test_shift.vim
@@ -111,3 +111,5 @@
   call assert_fails('2,1>', 'E493:')
   call assert_fails('2,1<', 'E493:')
 endfunc
+
+" vim: shiftwidth=2 sts=2 expandtab