Improvements to tests

[iamdefinitelyahuman]

The Issues

• The tests use many fixtures that inherit one another - it's a very powerful setup but not easy to understand at first glance.
• conftest.py files are sometimes 3 folders deep, and individual tests declare their own fixtures
• Objects such as accounts are being imported that could instead be retrieved as fixtures
• Test file organization could be improved

How to Fix

• [ ] Add verbose comments within tests/conftest.py explaining what each fixture does
• [ ] Reorganize fixtures - avoid declaring them within a test file, keep conftest.py files at most 1 subfolder beyond tests
• [ ] handle imports as fixtures where possible
• [ ] produce more subfolder README.md files to make tests easier to navigate

The ultimate goal is to make the test suite understandable even to someone who has never seen ZAP before, so it can be linked to from the Brownie docs as an example of what is possible.

[iamdefinitelyahuman]

In working on #20 I've discovered that some of the tests are broken because of breaking changes in Brownie. Along with a cleanup, the more important task is just to ensure that all tests are passing!

Marking this issue as high priority and adding it to the requirements to open source the repo.

[iamdefinitelyahuman]

Contracts and methods have been renamed per #21 but the overall structure of the tests is still lacking, and some of the name changes may have just made things even messier.