feat: Add Jest cheatsheet (#8034)

* feat: Add Jest cheatsheet

- Add jest cheatsheet

* Update jest links

* Move Jest cheatsheet into unit testing

Co-authored-by: LuigiImVector <LuigiImVector@users.noreply.github.com>

* Remove jest href

Co-authored-by: LuigiImVector <LuigiImVector@users.noreply.github.com>

Co-authored-by: LuigiImVector <LuigiImVector@users.noreply.github.com>

more/free-programming-cheatsheets.md

@@ -43,6 +43,7 @@
 * [SpringBoot](#springboot)
 * [SQL](#sql)
 * [Tensorflow](#tensorflow)
+* [Unit testing](#unit-testing)
 * [Webpack](#webpack)
 
 
@@ -385,6 +386,12 @@
 * [TensorFlow v2.0 Cheat Sheet](https://web.archive.org/web/20200922212358/https://www.aicheatsheets.com/static/pdfs/tensorflow_v_2.0.pdf) - Altoros (PDF) *(:card_file_box: archived)*
 
 
+### Unit testing
+
+* [Jest CheatSheet](https://devhints.io/jest) - devhints, Rico Santa Cruz (HTML)
+* [What is Unit testing](https://www.guru99.com/unit-testing-guide.html) - Thomas Hamilton (HTML)
+
+
 ### Webpack
 
 * [Webpack cheatsheet](https://devhints.io/webpack) - devhints, Rico Santa Cruz (HTML)