--- a/tests/test-merge-tools.t	Sat Nov 26 09:14:41 2016 -0800
+++ b/tests/test-merge-tools.t	Wed Nov 23 23:47:38 2016 +0100
@@ -1209,3 +1209,15 @@
   [1]
 
 #endif
+
+Verify naming of temporary files and that extension is preserved:
+
+  $ hg update -q -C 1
+  $ hg mv f f.txt
+  $ hg ci -qm "f.txt"
+  $ hg update -q -C 2
+  $ hg merge -y -r tip --tool echo --config merge-tools.echo.args='$base $local $other $output'
+  merging f and f.txt to f.txt
+  */f~base.?????? $TESTTMP/f.txt.orig */f~other.??????.txt $TESTTMP/f.txt (glob)
+  0 files updated, 1 files merged, 0 files removed, 0 files unresolved
+  (branch merge, don't forget to commit)