I think you're missing my main point: it's explained here https://www.ncover.com/support/docs/extras/code-coverage/understanding-branch-coverage but the gist is that line based coverage is over-counting: ``` if(A) // 100 lines of code else // 1 line of code ``` gives a line coverage of ~ 99% vs a branch coverage of ~50% (assuming `else` branch never covered in unittests)
What matters as far as bugs are concerned is that 50% of cases are covered. Increasing the size of the `if(A)` branch increases line coverage (which is irrelevant) but not branch coverage. On Sun, Feb 11, 2018 at 1:32 PM, Walter Bright via Digitalmars-d <digitalmars-d@puremagic.com> wrote: > On 2/5/2018 11:32 AM, Timothee Cour wrote: >> >> just filed https://issues.dlang.org/show_bug.cgi?id=18377: >> >> `dmd -cov -run main.d` shows 100% coverage; this is misleading since a >> branch is not taken: >> >> ``` >> void main(){ >> int a; >> if(false) a+=10; >> } >> ``` > > > Consider how -cov works today: > > 2| x = 3; y = 4; > 1| ++x; > > The first line has a count of 2, because there are two statements and each > contributes one increment to the line. > > 1| x = 3; // reference count > 2| if (true && false) c; > 3| if (true && true) c; > 1| if (false && b) c; > > The sequence points are each counted separately. So, by comparing with the > 'reference count', you can see which sequence points are executed. Also, if > one finds that unattractive, the code can be organized like: > > 1| if (true && > 1| false) > 0| c; > > and the separate counts will be revealed instead of aggregated. > > I agree that this is not ideal, however: > > 1. it works > 2. it is simple and robust > 3. the display to the user is simple > 4. it's easy to aggregate multiple runs together with simple text processing > code > 5. one can 'fix' it with a stylistic change in the formatting of the source > code > > Any further improvement would be a large increase in complexity of the > implementation, and I don't know of reasonable way to present this to the > user in a textual format. > > Is it worth it? I don't think so. Like builtin unittests, the big win with > -cov is it is *trivial* to use, which encourages its adoption. It's a 99% > solution, with 99% of the benefits, with 1% of the implementation effort. We > should be expending effort elsewhere than putting an additional 99% effort > to squeeze out that last 1% of benefit.
