NSIS: Assign a custom icon

Hello,

How to assign under NSIS a custom icon on for example, a file with a ".testica" extension?
Would you have a sample script to do this, please?

Thanks.

Write a DefaultIcon value to the registry.

Would you have a sample script with .testica extension, please?

Thanks.

You usually don't just assign a icon to a extension, you also assign a verb so the file can be opened in its application.