[Task] Add unit tests

**Task Description**
The plugin currently lacks any form of tests. It would be nice to start off by having unit tests.

**Deliverable(s)**
Basic unit tests setup and written for the handful of features that the plugin provides.

**Additional Context**
The unit tests [**in the core project**](https://github.com/tjtanjin/react-chatbotify) might be a good reference.