bug#25618: 25.1.91; More precise limit for tagging expensive tests

[Tino Calancha <tino.calancha@gmail.com>]

Prefer set a numeric limit of seconds than using the word 'few'.

For instance, in my box the test `cl-seq-test-bug24264' in
test/lisp/emacs-lisp/cl-seq-tests.el
takes 7 s.
With an explicit numeric threshold is easier to decide whether this test
must be tagged as expensive or not.

In following patch i define a few as 2-3 seconds.  Other people might
prefer 4-5 or even higher.
Please, suggest a proper value to consider a test as expensive.

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From 5671609ff5120ac7572b8a103a9aeb899542d47f Mon Sep 17 00:00:00 2001
From: Tino Calancha <tino.calancha@gmail.com>
Date: Sat, 4 Feb 2017 22:29:24 +0900
Subject: [PATCH] More precise limit for tagging expensive tests

* CONTRIBUTE (Testing your changes): Tag a test as expensive
when lasts longer than 2-3 seconds.
---
 CONTRIBUTE | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/CONTRIBUTE b/CONTRIBUTE
index e9a0341980..155b7ef762 100644
--- a/CONTRIBUTE
+++ b/CONTRIBUTE
@@ -273,7 +273,7 @@ http://www.gnu.org/software/emacs/manual/html_node/ert/
 or run 'info "(ert)"' for for more information on writing and running
 tests.
 
-If your test lasts longer than some few seconds, mark it in its
+If your test lasts longer than 2-3 seconds, mark it in its
 'ert-deftest' definition with ":tags '(:expensive-test)".
 
 To run tests on the entire Emacs tree, run "make check" from the
-- 
2.11.0

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In GNU Emacs 25.1.91.1 (x86_64-pc-linux-gnu, GTK+ Version 3.22.7)
 of 2017-02-04
Repository revision: 5e921112680f96d3ed94faf7dcf257e07f92d74b