Add Unit Testing with Pest

[erseco]

We need to add unit testing capabilities using Pest for the wp-decker repository to enhance our test suite and improve code reliability.

Tasks:

• Install and configure Pest in the project.
• Convert or add existing PHPUnit test cases to Pest format (if applicable).
• Create an initial set of unit tests for critical functionality using Pest.
• Update the project's documentation to include instructions for running Pest tests.
• Ensure that Pest tests run successfully in the existing CI/CD pipeline.

Benefits:

• Cleaner, more readable tests with a modern syntax.
• Improved developer experience and productivity.
• Increased test coverage and reliability of the codebase.

References:

• Pest Documentation

Feel free to adjust the tasks or add any specific details relevant to your project!