Add unit tests

Problem/Motivation

The module "paragraph_view_mode" for Drupal lacks PHPUnit tests, which are crucial for ensuring code quality and stability. Adding PHPUnit tests will help in verifying the functionality of the module and prevent regressions.

Steps to reproduce

- Install the "paragraph_view_mode" module on a Drupal instance.
- Attempt to execute PHPUnit tests by running `phpunit` in the module's directory.
- Notice the absence of any PHPUnit tests, leading to a gap in test coverage.

Proposed resolution

The proposed resolution is to develop PHPUnit tests for the "paragraph_view_mode" module. These tests should cover critical functionalities and edge cases to ensure robustness and reliability.

Remaining tasks

- Identify key functionalities and edge cases that need test coverage.
- Write PHPUnit tests to cover the identified areas.
- Ensure test coverage for both positive and negative scenarios.
- Integrate PHPUnit tests into the module's continuous integration pipeline for automated testing.

User interface changes

There are no user interface changes associated with this task.

API changes

There are no API changes associated with this task.

Data model changes

There are no data model changes associated with this task.