[Phase 1] Refactor 0x04h-Testing-Code-Quality.md

[cpholguera]

1. Go through each test case (1 MR per chapter)
2. Extract any general information and put it to the theory overview

• Each chapter must have a “## Overview” section and then several “## Testing …(MSTG-XXX-YY)” sections

• Strategy 1: move theory to chapter overview

• Strategy 2: move theory to general chapter overview

3. Only leave a test description on each test (see notes)

Notes:

• Follow the style guide
• If it helps you may already “pre-split” some tests by using:
  • “### “ subsections (example)
  • or “-” bullet point lists if there’s not enough details yet (example, right before the linked test there’s a list with several “- Check …”).

[iotaaxel]

Working on this.