[SystemSafety] MC/DC coverage assumptions
Steve Tockey
Steve.Tockey at construx.com
Wed Feb 28 16:33:10 CET 2018
Derek,
What do you mean by:
³The MC/DC coverage numbers were a lot better than the statement and
branch coverage. This is obviously a mistake, at best they can be
as good as.²
What does ³coverage number² mean here? More defects revealed? More test
cases required?
Thanks,
‹ steve
-----Original Message-----
From: systemsafety <systemsafety-bounces at lists.techfak.uni-bielefeld.de>
on behalf of Derek M Jones <derek at knosof.co.uk>
Organization: Knowledge Software, Ltd
Date: Wednesday, February 28, 2018 at 6:35 AM
To: "systemsafety at lists.techfak.uni-bielefeld.de"
<systemsafety at lists.techfak.uni-bielefeld.de>
Subject: [SystemSafety] MC/DC coverage assumptions
All,
I was recently reading a paper that compared unit testing of
industrial embedded software with some open source programs.
The comparison included a table of statement, branch and MC/DC coverage,
items in the table included: aerospace software, automotive software and
subway signal software
The MC/DC coverage numbers were a lot better than the statement and
branch coverage. This is obviously a mistake, at best they can be
as good as.
I emailed the authors, who have been very prompt replying.
The latest reply was a bit surprising.
The algorithm they used for MC/DC assumes that a function containing
a single branch (e.g., an if-statement with no else part) and
the test involves a single condition (i.e., no AND or OR conditions),
then 100% MC/DC coverage is assumed, even if 100% branch coverage is
not obtained.
Sounds like a mistake in their algorithm. However, they claim there is
some amount of existing practice and even call out Testbed as
behaving like this (I don't have a copy to check this out).
Somebody please tell me that this is not an assumption made by
commercial packages when calculating MC/DC coverage.
The authors admit that MC/DC coverage cannot be better than
statement and branch coverage, and admit the current presentation
of MC/DC coverage in the table could be misleading. They are going
to release a version with corrected data.
--
Derek M. Jones Software analysis
tel: +44 (0)1252 520667 blog:shape-of-code.coding-guidelines.com
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