specify appsettings while adding database migration

appsettings files

1. appsettings.json
2. appsettings.Production.json
3. appsettings.Test.json
4. appsettings.Debug.json

all for specific environment but first for common settings.

appsettings.json file does not contain connection string, since each environment has its own db.

running add-migration mig-1 obviously complains that

Could not find a connection string named 'ConnectionString'.

How can i specify connection string to be taken from appsettings.Test.json instead of default one (appsettings.json)