Build custom frontend test mapping solution

Summary

Build a coverage-based test mapper that generates source-to-test mappings for frontend code, similar to crystalball's coverage strategy for Ruby/RSpec. This enables better analytics and lays the groundwork for future feature category attribution.

Problem

Without test mapping:

• Cannot attribute coverage to specific tests
• Cannot determine which tests cover which files
• Limited analytics value (no team/category ownership)
• No foundation for future feature category support

With test mapping:

• Source file > test file relationships
• Better coverage analytics by directory/component
• Foundation for adding feature categories later
• Ability to identify uncovered or under-tested code paths

Proposal

Create a custom Jest reporter that extracts test-to-source mappings from existing coverage data, following crystalball gem's coverage strategy pattern.