Implementation of tests for the interoperability countries selection screen...

Implementation of tests for the interoperability countries selection screen (EXPOSUREAPP-2439) (#1140)

* Added initial set of viewModel tests

Signed-off-by: Kolya Opahle <k.opahle@sap.com>

* Fail tests on unexpected null.

Co-authored-by: Matthias Urhahn <matthias.urhahn@sap.com>