js: add Jest notes

Programming_Languages/JavaScript/Syntax/Testing_with_Jest.md

@@ -0,0 +1,19 @@
+---
+categories:
+  - Programming Languages
+tags: [javascript, testing]
+---
+
+# Testing with Jest
+
+## Mock a function
+
+## Mock a class/module
+
+## Check that a function has been called within another function
+
+## Mock a function that needs to be called within another function
+
+## Mock a function that takes arguments
+
+## Mocking network requests