Step 3 - React tutorial: Testing

### Step 3 in the "React, TypeScript, and TDD" tutorial

Test-first development with Jest and Enzyme integrated into the IDE.

00:00 - Start
00:12 - Show "old school" running Jest tests in an npm tool window
00:39 - Add a Jest run configuration with a watch
00:56 - Run the tests under that run configuration with dedicated testing tool window
01:12 - Click error to open test file on the line with the failure
01:32 - Get into "TDD mode": code on left, tests on right, test output at bottom
02:05 - Install Enzyme
02:54 - Write a new test to test the rendering of the heading
03:00 - Get IDE to fix a missing import
03:10 - Reformat code to correct inconsistent quote style
03:33 - See TDD in action with a code change that breaks the tests
04:00 - Write a failing test for a new feature
04:10 - Implement the feature, the test now passes

More on this tutorial step: