You should always write tests. To fully understand how to write production level applications in any language you should be able to write unit tests. Some people go to the extreme of doing Test Driven Development (TDD). TDD advocates that you should write tests before you write the code. This can be a good approach when trying to write code that can be easily tested. Yet I find that TDD is a lot like agile; a lot of people say they do it but in reality they do some sort of hybrid version.
The main goal of every startup is to make money. Every part of the organization should be driven to create money for the company. This means creating products that users want to buy while decreasing the cost to produce the product all in a timely manner.
In a technology startup the product to deliver in many cases is code. The beginning phases of this process involve a lot of late nights, rapid development, and manual processes.
In the past I have written about what a microservice architecture looks like and some of the tradeoffs that come with it. One of the biggest gains this architecture brings you is the ability for many people to be working on different projects at the same time. Inevitably the services you are writing will be used or you may need to consume someone else’s API to get your work done.