Reorganize the testing module

[jhlegarreta]

What would you like to see added in this software?

Following the decision in issue #63, tests dwell outside the package source folder. As more files are added or more tests are needed, it may become a little bit difficult to tell which test file corresponds to what module/feature.

Do you think that replicating the src module structure would be beneficial?

Do you have any interest in helping implement the feature?

Yes

Additional information / screenshots

N/A.