starting from baseline, implement few real tests, for unit testng and integration

[volodymyrss]

• there could be there is some meaningful dummy-like query?
• we could install it as a requirement and test it with a another fixture. If it is possible.
• if not possible, the tests should be really considered an "integration", in sense that it will be run on a specific instance, deployed for review.
  • I.e. it will not work with github actions.
  • In this case, the backend access will be configured on defining the test.
  • You can test it while setting your own instance.
  • And we test it after deploying in unige and also regularly.

[volodymyrss]

please see @dsavchenko if this agrees with follow-up of #4 and #3

[dsavchenko]

Implemented in #8 I think