Ruby Test Impact Analysis

Datadog developed a Ruby library for test impact analysis to significantly reduce testing time. Initially, existing solutions like Ruby's Coverage module and TracePoint were explored but found to have high performance overhead. The team then built a custom solution by diving into the Ruby VM and using interpreter events (RUBY_EVENT_LINE) via C extensions. This custom approach achieved a 60-80% performance overhead, compatible with other coverage tools, and offered flexibility for future enhancements.