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_largefile.vim b/src/testdir/test_largefile.vim
index 68d6ec9..4d0e2f0 100644
--- a/src/testdir/test_largefile.vim
+++ b/src/testdir/test_largefile.vim
@@ -27,3 +27,5 @@
   call assert_true(fsize == 4000000000)
   call delete(fname)
 endfunc
+
+" vim: shiftwidth=2 sts=2 expandtab