Making automated tests

[callumrollo]

@MOchiara this PR adds automated tests that will run on each new PR. Have a look at the individual pieces that come together to make it work

[callumrollo]

You can see how the tests have already triggered. Learning points:

• note how the test directory is called "tests" and every file and function in it started with test
• I've added pytest to requirements-dev, as well as adding all the stuff that has been added to the regular requirements
• the file .github/workflows/tests/yml is what controls making these tests run on github on a variety of computers and pyhon versions

[callumrollo]

notice how it fails for python version 3.8. Can you work out why?

[callumrollo]

Try checking out the details of the failed tests

[callumrollo]

note how the tests trigger again after I made a new commit and pushed it

[MOchiara]

This looks faster than mine...

[callumrollo]

hmmm, what's the difference between the two?