Feature/add better tests for expressions (#380)

* Add tests for special cases for expressions

Author: patrick-tolosa

__TESTS__/unit/actions/Variable.test.ts

@@ -178,4 +178,10 @@ describe('Tests for Transformation Action -- Variable', () => {
 
     expect(url).toBe('https://res.cloudinary.com/demo/image/upload/$myexp_md:!my_file!_to_f/sample');
   });
+
+  it('Tests special cases are not modified in expressions', () => {
+    ['$myheight', '$heightheight', '$theheight', '$__height'].forEach((exp: string) => {
+      expect(Expression.expression(exp).toString()).toBe(exp);
+    });
+  });
 });