--- a/tests/test-grep.t	Wed Jul 11 21:35:31 2018 +0900
+++ b/tests/test-grep.t	Wed Jul 11 21:51:47 2018 +0900
@@ -424,12 +424,25 @@
   $ hg grep --all-files -r. mod
   um:1:unmod
 
+commands.all-files can be negated by --no-all-files
+
+  $ hg grep --config commands.grep.all-files=True mod
+  new:2147483647:modified
+  um:2147483647:unmod
+  $ hg grep --config commands.grep.all-files=True --no-all-files mod
+  um:0:unmod
+
 --diff --all-files makes no sense since --diff is the option to grep history
 
   $ hg grep --diff --all-files um
   abort: --diff and --all-files are mutually exclusive
   [255]
 
+but --diff should precede the commands.grep.all-files option
+
+  $ hg grep --config commands.grep.all-files=True --diff mod
+  um:0:+:unmod
+
   $ cd ..
 
 Fix_Wdir(): test that passing wdir() t -r flag does greps on the