Ask HN: How to convince management for building better software?

So this is very honest question that I have been thinking for a while. I work for an agency. We build and maintain web apps for companies, some of them are fairly complex e-commerce stuff. We don't have single line of test. Because of this, whenever we need to do some changes, it's been very difficult. It has been worse with that fact that we also work with outside freelancers.

I am trying to step up a bit and fix those things I can. Few things on my mind are: coding guidelines (best practices), PEP-8, code review, writing extensive tests, setting up CI server. (Please feel free to suggest more.)

Now all of these things will take some extra time, particularly writing tests. People in management are not technical, and they don't care as far as things are working. How do you convince them that doing above things will improve quality of our apps and are worth the time and resource?