Description

Currently our unit tests are disorganized and each test creates example StellarGraph graphs in different or similar ways with no sharing of this code.

This issue is to improve the unit tests by making functions to create example graphs available to all unit tests by, for example, making them pytest fixtures at the top level of the tests (see https://docs.pytest.org/en/latest/

For further development of the project, it would be great to have unit tests to ensure the project code does not break with further changes/improvements. The tests go under tests folder in 2.0 branch where Python 3+ porting is happening.

In def generate_masks(N, s, p1):

Couldn't find what does N,s,p1 stands for in the code. I assume N stands for the number of filters generated? Since variable names don't imply their purpose, Commenting on its purpose or what it stands for would be great.