I\'ve always used Jasmine for my unit tests, but recently I started using Istanbul to give me code coverage reports. I mean I get the gist of what they are trying to te
Running istanbul should also produce an HTML file for the report (should be in the coverage folder). This HTML should give you drill-down information when you click on files/folders.
The percentage of functions covered is calculated by the number of functions that were called during tests, divided by total number of functions. Same goes for lines and statements (which will usually be close to each other unless you have very long statements).
Branches mean decision points like if-else
blocks. For example, say your code only contains one if-else
statement, and your tests only pass through the if
part but not the else
part, then your branches percentage should be 50%.
Hope that makes things clearer.
Adding to the previous answers
The %Statements is calculated by taking a percentage of the number of statements covered by your test e.g 12/18 * 100 = 66.67%. This means that your test covered only 66.67%.
The %Branch is also calculated in the same way. Same for your %Functions and %lines.
In your project root directory, there is a coverage folder that contains HTML output of your test. Click on it and view it in the browser. You should see something like this
Image showing the output of your test results
I hope this helps you understand it better.
There are a number of coverage criteria, the main ones being:
For each case, the percentage represents executed code vs not-executed code, which equals each fraction in percent format (e.g: 50% branches, 1/2).
In the file report:
'E'
stands for 'else path not taken', which means that for the marked if/else statement, the 'if' path has been tested but not the 'else'.'I'
stands for 'if path not taken', which is the opposite case: the 'if' hasn't been tested.xN
in left column is the amount of times that line has been executed.This has been verified for Istanbul v0.4.0, I'm not sure if this still applies for subsequent versions, but being that library is based on solid theoretic principles, behavior shouldn't change too much for newer versions.
It also provides some color codes -
Pink: statements not covered.
Orange: functions not covered.
Yellow: branches not covered.
Full Istanbul docs here:
https://istanbul.js.org
For more in-depth theory on code coverage:
https://en.wikipedia.org/wiki/Code_coverage
Hope it helps!