Authentication Database 'test' against 'admin' (?)

Using the MongoDB Atlas to get the string connection, it use ‘test’ as Authentication Database for all cases (mongo shell, application, and compass).

Ex:
mongo “mongodb+srv://mflix-mndvv.mongodb.net/test” --username
mongodb+srv://admin:@mflix-mndvv.mongodb.net/test?retryWrites=true
mongodb+srv://:@mflix-mndvv.mongodb.net/test

And it works for mongo shell and application, but doesnt work for compass. I lost some time to find out it, and when I change the Authentication Database to ‘admin’ it works for all cases.

Did I do something wrong?
What/Where is the ‘test’ database?

Ernesto

It is default DB in mongodb
When you don’t specify DB name in mongo command it will connect to test
use db command to switch the DB

C:\Users>mongo
MongoDB shell version v4.0.5
connecting to: mongodb://127.0.0.1:27017/?gssapiServiceName=mongodb
Implicit session: session { “id” : UUID(“c65defd7-2517-4864-b218-d521b20e8737”) }
MongoDB server version: 4.0.5

db
test
show collections
show dbs
admin 0.000GB
config 0.000GB
local 0.000GB
use admin
switched to db admin
db
admin