Set up proper testing

[nic-barbara]

We should have a file for each network in the test/ folder which tests:

• Forward pass runs without error.
• Backwards pass (computing gradients) runs without error.
• Check SDP for behavioural constraint from a randomly-sampled model (or a number of randomly-sampled models).
• Test the above 3 tasks with all combinations of input options (if relevant).

We can then use this to set up a proper CI/CD pipeline for this repository.