Make it easier to run the tests

[robdimsdale]

I am currently trying to submit a PR to this repo, but it is not easy to run the tests.

Ideally, I would like a script to run (e.g. ./scripts/test) but failing that even some documentation on the README would be great.

I'm happy to tackle this once we decide on what we want.

[robdimsdale]

I wonder whether this will be naturally resolved when we implement the Stack Description RFC

[sophiewigmore]

Agreed that this repo will change quite a bit as the stacks descriptor work, #133, and paketo-buildpacks/rfcs#197 all land, the structure of the repos will be different. However, we should keep this issue in mind when creating new workflows.

[ryanmoran]

I also think the tests themselves should be refactored to align with what we did in the jam create-stack test suite.

That test suite was derived from some refactoring I had done on this other branch of this repo to make the bionic tests a bit easier to deal with. For instance, the base stack test suite was updated use the new matchers I introduced in the jam integration suite.