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_jumps.vim b/src/testdir/test_jumps.vim
index 5a3717d..5b46adc 100644
--- a/src/testdir/test_jumps.vim
+++ b/src/testdir/test_jumps.vim
@@ -1,3 +1,5 @@
+" Test for '' mark in an empty buffer
+
 func Test_empty_buffer()
   new
   insert
@@ -9,3 +11,5 @@
   call assert_equal(1, line("''"))
   bwipe!
 endfunc
+
+" vim: shiftwidth=2 sts=2 expandtab