ActiveRecord::Base.establish_connection doesn't actually test that your connection spec can connect to the database. You need to ask for a connection to test that explicitly.

connection_established.rb

ActiveRecord::Base.establish_connection

# Check if the spec passed to `ActiveRecord::Base.establish_connection` can connect to the database.
#
# @return [true] if an active connection can be made to the database using the current config.
# @return [false] if an active connection cannot be made to the database.
def connection_established?
  begin
    # use with_connection so the connection doesn't stay pinned to the thread.
    ActiveRecord::Base.connection_pool.with_connection {
      ActiveRecord::Base.connection.active?
    }
  rescue PG::ConnectionBad => error
    false
  end
end

trigger_connection.rb

ActiveRecord::Base.establish_connection
ActiveRecord::Base.connected? # false

ActiveRecord::Base.connection.active? # true