How do I test a paragraph bundle entity reference with Behat?
I needed something similar so I implemented a context for paragraph support.

Install using composer require miiimooo/behat-tools

The follow the installation and usage here: https://github.com/miiimooo/behat-tools

In your feature you can then write:

Feature: Content
  @api
  Scenario: Paragraph creation through Drupal 8 API

    Given a "my_paragraph_type" paragraph named "my_arbitrary_name":
      | title             | Lorem ipsum |

    Given I am viewing a "page" content:
      | title            | Dolor sed         |
      | field_paragraphs | my_arbitrary_name |