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_interrupt.vim b/src/testdir/test_interrupt.vim
index 111752d..21ff097 100644
--- a/src/testdir/test_interrupt.vim
+++ b/src/testdir/test_interrupt.vim
@@ -25,3 +25,5 @@
   call assert_equal(0, s:bufwritepost_called)
   call assert_equal(0, filereadable('Xfile'))
 endfunc
+
+" vim: shiftwidth=2 sts=2 expandtab