node.js/express unit testing -- safe to ignore configuration files in Istanbul?

I'm sorry if this is a rather ambiguous question -- I used to be one of those devs who is far too lazy to write unit tests, but now that I'm working on a pretty large project, I've come to see the value in them.

I've set up istanbul with some (hopefully) sensible thresholds:

const options = {
    codeCoverage: {
        reporters: ['lcov', 'text-summary'],
        thresholds: {
            global: { statements: 80, branches: 80, functions: 80, lines: 80 },
            each: { statements: 50, branches: 50, functions: 50, lines: 50 }
        }
    }
};

But this causes my test task in gulp to fail, because istanbul reports that my config files (those that set up middleware and various other boilerplate-ish stuff) aren't covered.

I've tried searching for hours, but haven't found any guidelines as to which code is safe to ignore -- I've only been told by more senior developers that it's necessary to test controllers and so on, but not config files -- which are pretty much impossible to test anyway. Feedback would be much appreciated!