Wrong branch coverage percentage

[andreamatt]

🐛 Bug Report

Jest reports wrong branch coverage percentage. Uncovered lines are correct.

To Reproduce

EDIT

• added console.log(1/2) so that branches are not empty. Still wrong/unexpected results

function foo(a, b) {
    if (a && b) {
        console.log('1');
    } else {
        console.log('2');
    }
    return 0;
}

tests with only 1 function call
foo(0,0) gives 50%
foo(0,1) gives 50%
foo(1,0) gives 75%
foo(1,1) gives 75%

Uncovered lines are always correct and if both branches are covered it gives 100%.

Expected behavior

There is only 1 'if-else', so branch coverage should always be a multiple of 0.5.

Run npx envinfo --preset jest

System:
    OS: Windows 10
    CPU: (4) x64 Intel(R) Core(TM) i3-7100U CPU @ 2.40GHz
Binaries:
    Node: 10.10.0 - D:\Software\nodejs\node.EXE
    npm: 6.4.1 - D:\Software\nodejs\npm.CMD

[rickhanlonii]

Hey @andreamatt, we use istanbuljs for coverage reporting, they may be able to explain better

[github-actions]

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