Fix test deprecation warnings

[louis-antonopoulos]

This PR:

• Addresses two different deprecation warnings that appear when running tests:

DEPRECATION WARNING: The `exist` matcher overrides one built-in by RSpec; 
use `expect(Pathname.new(path)).to exist` instead

DEPRECATION WARNING: Using legacy connection handling is deprecated. 
Please set `legacy_connection_handling` to `false` in your application.

[louis-antonopoulos]

I believe CI is failing here due to the issues resolved by #1017.