Testing a Rails Application with Multiple Databases

I have a rails application which uses two databases in production environment, Users and Process. The Users model uses this customized ActiveRecord class:

class UserActiveRecord < ActiveRecord::Base
    establish_connection "#{Rails.env}_users_db"
end

class User < UserActiveRecord
    ...

Notice that the connection to a specific database is established depending on the environment. To simplify things, in the testing environment I have a single database with all the tables from the two production databases, and my database.yml file looks something like this:

test:
    adapter: postgresql
    database: db_test
    host: localhost
    pool: ...
    timeout: ...
    username: ...
    password: ...

test_users_db:
    adapter: postgresql
    database: db_test  <--- Notice that this is the same database only in test env
    host: localhost
    pool: ...
    timeout: ...
    username: ...
    password: ...

The application runs fine in production, but when I run any test that refers to the User class, the test blocks at the exact point where User is used and nothing happens, it doesn't show any error, it doesn't exit, it just keeps waiting.

I double-checked and the table USERS exists in the test database, in fact if I delete it manually I get the error that the table doesn't exists and when I create it again I get the same behavior reported in the previous paragraph.

I don't have a clue why this is happening, any idea on how can I solve this issue? or how can I debug it so that I can get to the root of the problem? Any additional details will be posted as required.