Fix tests for #1886 with ActiveRecord 3.x

We didn't properly call the method to test, which lead to a failing
test. However, this couldn't be properly displayed on ruby
installations with an ActiveRecord 3.x installed, as the inspect in
the after test part, tried to examine the table, which (obviuosly)
raised a NotConnected exception.

By calling the method the right way, we fix the test and hence also
fix the failing inspection.