How to test new integration locally while developing?

I am trying to develop a new integration but find it hard to understand the development process. I am used to run my code often and quickly to test it but using the dev container process and developing in the core project all I can see is some unit tests to run which take ages to start.
What is the recommended process? develop offline in a separate repo and then move the final code into the integration structure for testing?

For me, i am writing the code, starting ha core inside docker, testing it and stopping it to change the code if needed. It takes around 5 seconds to start up home assistant.

To make your life simpler, you have to develop an independent separate api package, run it directly with python console without having any interaction with home assistant. When you are done with it, publish it to pypi and declare a dependency to your new pypi package inside home assistant integration.

If I understand correctly, you add your component to the configuration file, then go to the terminal and start HA and then monitor the logs to see whether it fails or what it outputs?
Are you able to integrate the frontend with the core instance you are starting?

I am using visual studio code and there are docker actions to run home assistant core. You can open normal ha website, add your integration as you do normally or rely on yaml based setup. Not using any terminal to run ha core