Update base test case

[dingo-d]

Description

Add Yoast's TestCase as the base test case in both unit and integration tests inside Pest.php file.

This will expose all the useful Brain Monkey mocking functions in the unit tests without explicitly importing it (test case has it covered).

Types of changes

New feature (non-breaking change which adds functionality)

Checklist:

• [x] My code is tested.
• [x] My code follows the code style set by the project.
• [x] I've included documentation for the changes.

[codecov-commenter]

Codecov Report

Merging #6 (61667dc) into main (c4da2e6) will not change coverage. The diff coverage is n/a.

@@            Coverage Diff            @@
##               main       #6   +/-   ##
=========================================
  Coverage     90.07%   90.07%           
  Complexity       38       38           
=========================================
  Files             1        1           
  Lines           131      131           
=========================================
  Hits            118      118           
  Misses           13       13           

Flag	Coverage Δ
unittests	90.07% <ø> (ø)

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