Create a `jest` based runner

[3rd-Eden]

This ticket tracks the creation of a jest based runner. In order to integrate a test runner our system makes the following assumptions:

• There is an API that can be required.
• Importing of test files prepares or executes the tests.
• There is an API, method that we can execute to run the tests or listen to test completion.
• No child process / forking / spawning, or file system operation supported.

Currently jest executes the tests through their jest CLI. There is no programmatic API documented that we can use. This doesn't mean it's impossible to integrate. In the last few months, they started extracting bit's of the CLI into a dedicated jest-core package that would eventually become an API https://github.com/facebook/jest/pull/7696 this work is currently tracked in https://github.com/facebook/jest/issues/5048. When this work is completed it should become a lot easier to integrate jest as test runner.

Acceptance Criteria

• [ ] Users can select jest as test runner.
• [ ] Custom jest configuration can be supplied using --jest.{key} {value} CLI flags.
• [ ] Example is added to our examples folder.
• [ ] Documentation and new unit tests have been added.

[shwanton]

Adding jest runner support would be awesome!

Could React Native Testing Library be used even w/o the jest runner?

[3rd-Eden]

@shwanton I haven't tried it yet, so I can't really comment on it. Have you given it a go?

[shwanton]

I have, but mostly for snapshot tests. However w/ RN there is still all the native mocks that need to happen so having it run in a real simulator sounds like a great solution.