ACP2E-4907: Document DataProvider/TestWith data injection into fixtures

[bubasuma]

Purpose of this pull request

This pull request documents the dataset reserved fixture alias (added for ACP2E-4883), which exposes the current PHPUnit #[DataProvider]/#[TestWith] row to #[DataFixture] attributes via $dataset.key$. This lets a single parameterized test replace multiple near-identical test methods that only differ in fixture configuration.

• Adds a "Supply DataProvider or TestWith data to a fixture" reference section to the DataFixture attribute doc
• Adds an "Avoid duplicating tests that only differ by fixture data" best practice to the data fixtures guide

Affected pages

• https://developer.adobe.com/commerce/testing/guide/integration/attributes/data-fixture
• https://developer.adobe.com/commerce/testing/guide/integration/data-fixtures-guide

Links to the public Commerce codebase

• magento/magento2@8a05e77

[github-actions]

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Generated: 2026-09-15T16:15:30.057Z
Mode: Full Linting (all rules + dead links check)
Target Directory: /home/runner/work/commerce-testing/commerce-testing

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Files to process: 2


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[github-actions]

🔍 Linter Report

Click to expand full report

═══════════════════════════════════════════════════════════════
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Generated: 2026-09-15T16:38:41.071Z
Mode: Full Linting (all rules + dead links check)
Target Directory: /home/runner/work/commerce-testing/commerce-testing

───────────────────────────────────────────────────────────────

Files to process: 2


═══════════════════════════════════════════════════════════════
                        SUMMARY
═══════════════════════════════════════════════════════════════

  📁 Files processed:    2
  📄 Files with issues:  0
  ❌ Total errors:       0
  ⚠️  Total warnings:     0
  📋 Total issues:       0

Result: ✅ PASSED - All files passed linting successfully!

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