--- a/tests/test-command-template.t	Wed Mar 21 12:06:18 2018 +0900
+++ b/tests/test-command-template.t	Mon Mar 19 00:23:20 2018 +0900
@@ -4166,6 +4166,15 @@
   1
   0
 
+  $ hg log -l1 -T '{ifcontains("branch", extras, "t", "f")}\n'
+  t
+  $ hg log -l1 -T '{ifcontains("branch", extras % "{key}", "t", "f")}\n'
+  t
+  $ hg log -l1 -T '{ifcontains("branc", extras % "{key}", "t", "f")}\n'
+  f
+  $ hg log -l1 -T '{ifcontains("branc", stringify(extras % "{key}"), "t", "f")}\n'
+  t
+
 Test revset function
 
   $ hg log --template '{rev} {ifcontains(rev, revset("."), "current rev", "not current rev")}\n'