complete coverage of javascript coalesce

[kellyselden]

is it possible to get complete coverage of this line?

this.imageFactory = stuff.imageFactory || function() { return new Image() };

it's a hack of dependency injection. it's never evaluated to false, but the right-most is always true.

[tntim96]

You won't get 100% branch coverage unless it evaluates to both true and false.

[kellyselden]

Is this an issue you deal with often? or do you write your code without coalescing for better code coverage?

[tntim96]

I'm open to suggestions for detecting and avoiding this. A couple of options are:

• Ignoring certain lines of code as JSCoverage does
• You could manually put in a post process step to remove that part of the JSON

[tntim96]

I could add an switch which could make the branch coverage check if the compare types are boolean at run-time. A bit more difficult, but the parser could try to determine if the result of the evaluation is an assignment, and only generate the above logic in that scenario...is that what you're after?

[kellyselden]

I think that would be perfect. I've been thinking about how you would write that, how to know whether the right side is a bool or not. This line would be a problem in my mind:

var oldFunc = null;
var newFunc = new function() { };
this.test = oldFunc || newFunc;

Knowing the types of those vars when on the third line seems difficult to me, but your parser may be smarter than I think.

[eidng8]

This kind of shortcut is widely used in JS. I think you can safely ignore the outcome in coverage, as long as it's an assignment. BTW, the boolean checking may not be proper since boolean, albeit true or false, are sometimes desired. Afterall, it's null coalescing.

[eidng8]

Second though, it may be much easier to implement a option or switch to completely turn off the true false check

[tntim96]

OK, I've put in a CLI option, --detect-coalesce, to exclude coalesce from conditional coverage. At this stage it simply checks for an || operator in an assignment. The tests scenarios are in BranchHelperTest.

You can try the latest build at https://drone.io/github.com/tntim96/JSCover/files. Let me know if you find any issues, otherwise I'll release in a week or so.

[eidng8]

It works. Thanks a lot.

btw, --detect-coalesce may be confusing. Wouldn't --allow-coalesce or --ignore-branch-assign be better? Or something else, sorry for my poor English. 😏

[tntim96]

Great.

Yes the naming is difficult, but it was the best I could think of that wasn't too long (e.g. --ignore-branch-on-null-coalesce). It's not exactly a branch but a condition, and other branch assignments won't be ignored, so I thought I'd just keep it short a leave the description in the manual and help documentation.