Add instructions on how to run the tests

[amcewen]

With #37 and #15 we now have some test infrastructure.

How do I run the tests? I'd expect there to be a line or two of description in README.md to give me the basics, in the same way that there are instructions for setting up the database or running the development server.

For extra credit, a section explaining how to add a new test ("create a file in tests, you can use X as a template; then add any data into the test database by creating a file like Y in Z") would encourage more of us to write more tests 😁

[JackiePease]

I have updated the README.md file to add the following lines:
npm run test (or npm tests or npm t) runs .js files in the test subfolder. You can use one of the existing files e.g. app.test.js as a template (first set the NODE_ENV environment variable to 'testing' and run npx knex install:latest to use the latest version of the test database)
However, there don't seem to be any relevant migrations to set up data in the 'testing' database at the moment. Will look into further.

[amcewen]

Should this still be open, or are the instructions in the README.md and documentation/testing.md sufficient?

(I had to remove the api/node_modules folder to get npm run test-api to run for me, otherwise it failed when trying to run some test in api/node_modules/a-sync-waterfall/test.js - which presumably it shouldn't have been running)