docs: matchMedia mock implementation to testing docs

[bwcr]

📝 Description

Added a mock implementation for matchMedia to the testing documentation. matchmedia is needed to make the unit test work.

⛳️ Current behavior (updates)

I am currently modifying the testing documentation to support unit tests with testing-library and jsdom

🚀 New behavior

Based on the tutorial, it somehow returns TypeError: window.matchMedia is not a function, so I decided to add matchmedia function to the setup test file

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Latest commit: 4f3316a

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