Coverage gives a false positive with a || branch

[ljharb]

Expected Behavior

The below code will not have 100% coverage, because keys.length is never > 1, so the "if" branch of that condition was never exercised.

Observed Behavior

The below code is reported as having 100% coverage.

Bonus Points! Code (or Repository) that Reproduces Issue

function test(options = {}) {
  const keys = Object.keys(options);
  if (keys.length > 1 || (keys.length === 1 && keys[0] !== 'something valid')) {
    return false;
  }
  return true;
}
test();
test({});
test({ 'something valid': true });

Forensic Information

Operating System: Mac OS
Environment Information: node 10.1, npm 5.6.

[ljharb]

Specifically, if I remove this line then I should not have 100% coverage anymore.

[coreyfarrell]

@ljharb I've done some testing with nyc@12.0.2. See https://gist.github.com/coreyfarrell/1a98d9a4d2cbf46854f2c9936dab0c77 for a slightly modified version of your test function and how that is instrumented by NYC. As far as I can tell the coverage data for the if branch is correct, it reports if you fail to hit both true and false conditions. The issue is for the binary-expr branches, it looks like we're counting when each sub-expression is hit regardless of result instead of counting how many results were truthy and how many weren't.

I have to think about this more to determine a good solution which would avoid breaking stuff like txt = txt || 'default';.

[ljharb]

Thanks, that sounds like progress to me :-D

[ljharb]

bump.

[ljharb]

bump

[coreyfarrell]

@ljharb I still don't have a solution for this bug but the stale bot will not be touching this issue again.