When I write unit tests, I begin to think of what could go wrong inside my code, it helps me to improve code design, and apply Single Responsibility principle. Also, when I come back to modify the same code few months later, it helps me to confirm that existing functionality isn't broken.

There is a trend to use pure functions as much as you can (serverless apps). Unit testing helps me to isolate state and write pure functions.

Specifically, we will have a Web API service that will be very thin. Its main responsibility will be marshalling web requests/responses and calling an underlying API that contains the business logic.

Write unit tests for the underlying API first and if you have sufficient development time, you need to write tests for the thin Web API service as well.

TL;DR, unit testing helps improve quality of code and helps make future changes to code risk free. It also improves readability of the code. Use tests instead of comments to make your point.

When I write unit tests, I begin to think of what could go wrong inside my code. It helps me to improve code design and apply the single responsibility principle (SRP). Also, when I come back to modify the same code a few months later, it helps me to confirm that existing functionality isn't broken.

There is a trend to use pure functions as much as you can (serverless apps). Unit testing helps me to isolate state and write pure functions.

Specifically, we will have a Web API service that will be very thin. Its main responsibility will be marshalling web requests/responses and calling an underlying API that contains the business logic.

Write unit tests for the underlying API first and if you have sufficient development time, you need to write tests for the thin Web API service as well.

TL;DR, unit testing helps improve quality of code and helps make future changes to code risk free. It also improves readability of the code. Use tests instead of comments to make your point.