Testing - How to test if you are actually testing the code?

Question

I was thinking about unit tests and code coverage, and I came up with this thought:

It is possible to have 100% code coverage and not test 100% of your code.

For example:

function myTestedFunction(){
    doSomething();
    doSomethingElse();
}

In this example, if I have a test that myTestedFunction calls doSomething, doSomethingElse(); will count as tested, even though it's not. Is there some way or library that will run your tests with each line removed? I feel like I'm describing it poorly.

I'm using Node.js at the moment, but I'm more curious if something like this exists.

So does anybody know of such a thing?

Thanks!

Answer 1

What you're talking about is called mutation testing, and there are a number of implementations available. I've not tried either, but there are at least two javascript versions:

• grunt-mutation-testing, and
• mutandis