Update TESTING.md

Author: adamint

TESTING.md

@@ -5,6 +5,7 @@ We use [Spek](https://github.com/spekframework/spek) to run unit tests.
 To run any test, you must have two environment variables, `SPOTIFY_CLIENT_ID` and `SPOTIFY_CLIENT_SECRET` set to a Spotify application in your current shell.
 
 `export SPOTIFY_CLIENT_ID=your_client_id`
+
 `export SPOTIFY_CLIENT_SECRET=your_client_secret`
 
 To run **only** public endpoint and utility tests, run `gradle check`