Add SlidingWindow unit tests

[nicola-corbellini]

We don't have unittests for the sliding window.
Can you point me where I could add those please @sanketsabharwal ?

[sanketsabharwal]

i'd recommend putting it under tests/data_model since our unit tests are currently defined for testing feature computations. curious, what would you like to test about the sliding window?

[nicola-corbellini]

That appending, resizing, indexing, printing and everything else.
The point of unittests is to test atomic functionalities of each class, hence I want to be sure to add new functionalities (e.g., .extend) without breaking anything

[sanketsabharwal]

@nicola-corbellini are you taking this up as well?

[nicola-corbellini]

Not yet, same as the other issue about the sliding window