As a Rails dev it's extremely rare for me to need some functionality that Ruby doesn't cover. If you're doing standard web development most likely you're gonna be fine with Ruby. I've been doing this with Ruby for around 8 years so I bumped into quite a few use cases...there are gems for all the standard things.
But yes outside web - data science, web crawlers etc...Python has the clear advantage.
You dont mock the db layer, i dont do that at least, hell no. Let the db be hit, check that the records it returns make sense. Thats how I roll at least.
Didn't want to aim at you with the reply, just remembered the collective delusion of 100% coverage unit testing zealots and how this would ironically fail to catch this.
You'd be surprised how far people go to shoot themselves in the foot.
I dont wanna sound negative but for some people giving up makes sense. Entrepreneurship could be extremely isolating and depressig, especially when its not working out, and not everyone wants a decade of failure after failure and missing out on other financial and social opportunities.
Yes, 3 years is pretty much a good way to measure if you have made it or not. Anything beyond that is pretty much a waste of time. Also, surrounding yourself with people of similar interests will keep you going. Currently, I have some great indie hacker friends on Twitter who keep me motivated.
What type of interview? If it's a Leetcode/Coderpad type of test where you're expected to deliver a working solution in 30-60 minutes definitely go with what you know best. No one cares if it's Ruby or Python. They want to see your code generally works.