feat: characterization tests and domain extraction for flight booking API

[martinov]

Summary

• Added characterization tests capturing existing behavior of all flight search and booking endpoints (happy paths, edge cases, quirks)
• Created behavior catalogs documenting every tested scenario for flights and bookings
• Extracted domain logic from monolithic flight-booking-api.ts into focused modules: pricing, search-flights, create-booking, update-booking, cancel-booking
• Introduced repository ports (FlightRepository, BookingRepository) with in-memory adapters

Test plan

• Run pnpm test in session-2/1-characterization-refactoring/ to verify all characterization tests pass
• Start the API server and run requests.sh to verify endpoints work end-to-end

[martinov]

Thanks for the refactor and characterization coverage - I found one blocker before merge:\n\n- Blocking: starts the server at module import time (). With multiple test files, Jest runs suites in parallel by default, so multiple workers try to bind and one fails with .\n - Repro: run

flight-booking-api-legacy@1.0.0 test
jest in (default config)\n - Result: one suite fails immediately on import due to port collision\n - Suggested fix: only start listening when the file is executed directly (not when imported by tests), and keep exporting for .\n\n- Non-blocking: hardcodes a booking ID (), so GET/PUT/DELETE usually fail unless that exact ID exists from an earlier run.

[martinov]

Posting a corrected version of my previous comment (formatting got mangled by shell interpolation):

Thanks for the refactor and characterization coverage - I found one blocker before merge:

• Blocking: session-2/1-characterization-refactoring/src/flight-booking-api.ts:86 starts the server at module import time (app.listen(...)). With multiple test files, Jest runs suites in parallel by default, so multiple workers try to bind :3000 and one fails with EADDRINUSE.

  • Repro: run npm test in session-2/1-characterization-refactoring/ (default config)
  • Result: one suite fails immediately on import due to port collision
  • Suggested fix: only start listening when the file is executed directly (not when imported by tests), and keep exporting app for supertest.

• Non-blocking: session-2/1-characterization-refactoring/requests.sh:17 hardcodes a booking ID (BK-1773732306909-1), so GET/PUT/DELETE usually fail unless that exact ID exists from an earlier run.