Update the [Systems and Testing] section of the documentation

[Akinbola247]

The Testing section of the documentation as well Systems section are not up to date, I'd like to work on it.
Here are the links to the sections that needs update: https://github.com/dojoengine/book/blob/main/src/cairo/testing.md#writing-integration-tests
https://github.com/dojoengine/book/blob/main/src/cairo/systems.md

[ponderingdemocritus]

Thank you - the plan is to go straight to the 0.3.0 docs, which is a bit of a change in how tests are written. You can see how they are written here: 0.3.0

Would you be able to tackle this?

[Akinbola247]

Yes, i can tackle it!