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_join.vim b/src/testdir/test_join.vim
index fdd9e05..8f7ccb6 100644
--- a/src/testdir/test_join.vim
+++ b/src/testdir/test_join.vim
@@ -444,3 +444,5 @@
   call assert_equal(['a', 'b c'], getline(1, '$'))
   bwipe!
 endfunc
+
+" vim: shiftwidth=2 sts=2 expandtab