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_window_cmd.vim b/src/testdir/test_window_cmd.vim
index 5506dbe..a352ae1 100644
--- a/src/testdir/test_window_cmd.vim
+++ b/src/testdir/test_window_cmd.vim
@@ -1,6 +1,6 @@
 " Tests for window cmd (:wincmd, :split, :vsplit, :resize and etc...)
 
-so check.vim
+source check.vim
 
 func Test_window_cmd_ls0_with_split()
   set ls=0
@@ -655,9 +655,7 @@
 
 func Test_window_prevwin()
   " Can we make this work on MS-Windows?
-  if !has('unix')
-    return
-  endif
+  CheckUnix
 
   set hidden autoread
   call writefile(['2'], 'tmp.txt')