patch 7.4.2086
Problem:    Using the system default encoding makes tests unpredictable.
Solution:   Always use utf-8 or latin1 in the new style tests.  Remove setting
            encoding and scriptencoding where it is not needed.
diff --git a/src/testdir/runtest.vim b/src/testdir/runtest.vim
index 559d5f8..e06e0cb 100644
--- a/src/testdir/runtest.vim
+++ b/src/testdir/runtest.vim
@@ -49,6 +49,14 @@
 " This also enables use of line continuation.
 set nocp viminfo+=nviminfo
 
+" Use utf-8 or latin1 be default, instead of whatever the system default
+" happens to be.  Individual tests can overrule this at the top of the file.
+if has('multi_byte')
+  set encoding=utf-8
+else
+  set encoding=latin1
+endif
+
 " Avoid stopping at the "hit enter" prompt
 set nomore