Add test for `react-native-typescript-screen`

[jsjoeio]

Summary

In order to save some time, I skipped writing a test for the react-native-typescript-screen template because it was taking too long. The test requires use of a spawn because we have to write test after the command is executed due to the hygen prompt.

Basic example

The test is stubbed out. We just need to spend the time figuring out how to do it.

Motivation

It's important to have integration tests for all our commands.

[jsjoeio]

This article might help: Node.js Child Processes: Everything you need to know