[SystemSafety] MC/DC coverage assumptions

[Steve Tockey]

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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