atom: Add snippet for Mocha test statement

atom/snippets.cson

@@ -19,3 +19,16 @@
 # If you are unfamiliar with CSON, you can read more about it in the
 # Atom Flight Manual:
 # https://atom.io/docs/latest/using-atom-basic-customization#cson
+
+'.source.js':
+  'mocha-test':
+    'prefix': 'describe'
+    'body': """
+import { expect } from 'chai';
+
+describe('$1', function() {
+  it('should $2', function() {
+    // test goes here
+  });
+});
+"""