[SystemSafety] MC/DC coverage assumptions

[Derek M Jones]

Dewi,

> The definition of Modified Condition/Decision Coverage is:
...
> In your example, the single condition would have to have been evaluated to
> both true and false to achieve MC/DC. This means that at least two test
> cases are required to achieve either MC/DC or branch coverage, but one test
> case would be sufficient to achieve statement coverage.

As Ian Broster's interesting reply shows, there are people out there who
have other ideas.

> I'd be astonished if a tool with the pedigree of LDRA Testbed got this
> wrong.

As would I.

Perhaps there is a compatibility flag, -do_what_broken_tool_does?

> 
> Dewi
> 
> Yours,
> 
> Dewi Daniels | Director | Software Safety Limited
> 
> Telephone +44 7968 837742 | Email d <ddaniels at verocel.com>
> ewi.daniels at software-safety.com
> 
> Software Safety Limited is a company registered in England and Wales.
> Company number: 9390590. Registered office: Fairfield, 30F Bratton Road,
> West Ashton, Trowbridge, United Kingdom BA14 6AZ
> 
> On 28 February 2018 at 14:35, Derek M Jones <derek at knosof.co.uk> wrote:
> 
>> 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
>> _______________________________________________
>> The System Safety Mailing List
>> systemsafety at TechFak.Uni-Bielefeld.DE
>>
> 

-- 
Derek M. Jones           Software analysis
tel: +44 (0)1252 520667  blog:shape-of-code.coding-guidelines.com