Added Landmark_model_test

[ItsAdityaKSingh]

Partly fixes #46

Describe the changes you have made in this PR - Added test for landmark model

[Aadeesh11]

Both LandMark and Location fromJson method is being tested in Beacon fromJson test. This can add redundancy. 😅

[ItsAdityaKSingh]

There shouldn't be a redundancy as there are separate models for fetching it; having particular tests could increase code coverage and test each of them particularly too.

[nb9960]

There shouldn't be a redundancy as there are separate models for fetching it; having particular tests could increase code coverage and test each of them particularly too.

But each field is already tested there too. I'd agreed to your statement if there would've other use cases for this model.
To reduce the redundancy what we can do is to just add validations here and PR #114 should use these. In any case, it would be better if you both collaborate and decide to go with one flow.

[ItsAdityaKSingh]

Sure @nb9960! I'll do the needful

[ItsAdityaKSingh]

Not necessary as PR #114 already handles it.