--- a/tests/test-evolve-templates.t	Fri Jun 16 09:22:39 2017 +0200
+++ b/tests/test-evolve-templates.t	Fri Jun 16 17:11:20 2017 +0200
@@ -117,6 +117,17 @@
   |
   o  ea207398892e
   
+
+(check json)
+
+  $ hg log -GT '{precursors|json}\n'
+  o  ["471f378eab4c5e25f6c77f785b27c936efb22874"]
+  |
+  | @  []
+  |/
+  o  []
+  
+
   $ hg up 'desc(A1)' --hidden
   1 files updated, 0 files merged, 0 files removed, 0 files unresolved
   working directory parent is obsolete! (a468dc9b3633)