tests: add a substitution for ENOENT/ERROR_FILE_NOT_FOUND messages Automatic replacement seems better than trying to figure out a check-code rule. I didn't bother looking to see why the error message and file name is reversed in the annotate and histedit tests, based on Windows or not. I originally had this as a list of tuples, conditional on the platform. But there are a couple of 'No such file or directory' messages emitted by Mercurial itself, so unconditional is required for stability. There are also several variants of what I assume is 'connection refused' and 'unknown host' in test-clone.t and test-clonebundles.t for Docker, FreeBSD jails, etc. Yes, these are handled by (re) tags, but maybe it would be better to capture those strings in order to avoid whack-a-mole in future tests. All of this points to using a dictionary containing one or more strings-to-be-replaced values.

--- a/tests/test-subrepo-svn.t	Sun Dec 03 20:55:35 2017 -0800
+++ b/tests/test-subrepo-svn.t	Sat Dec 02 19:33:34 2017 -0500
@@ -571,15 +571,9 @@
 Test forgetting files, not implemented in svn subrepo, used to
 traceback
 
-#if no-windows
   $ hg forget 'notafile*'
-  notafile*: No such file or directory
+  notafile*: $ENOENT$
   [1]
-#else
-  $ hg forget 'notafile'
-  notafile: * (glob)
-  [1]
-#endif
 
 Test a subrepo referencing a just moved svn path. Last commit rev will
 be different from the revision, and the path will be different as