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Home pricing rule engine with breakdown and override

seniorjava · AI-on
  1. 1Restate the problem in one line
  2. 2Sketch the data model yourself
  3. 3Ask AI for a skeleton ONLY
  4. 4Ask AI for a test plan ONLY
  5. 5Implement the core logic yourself
  6. 6Run the tests — verify, don't trust
  7. 7Ask AI for edge cases you missed
  8. 8Ask AI to review your code
  9. 9Make the final judgment yourself

Problem

Build a PricingEngine that prices a Home as final = base + renovation + riskAdjustment + marketAdjustment. Each component is produced by its own rule and recorded in a breakdown() map keyed by component name; the recorded components must always sum to the returned price. price(Home) returns the final int price. setOverride(int) sets a manual override that wins over the computed total — when an override is active, price() returns the override and the breakdown still sums to it. Model the rules as a list of strategy objects so each one contributes one labeled part.

iThe deal with the pair partner

The AI is deliberately fallible — it gives hints, not solutions, and sometimes proposes wrong code. It cannot touch your editor. Paste what you choose, then Run. Anything AI-derived stays UNVERIFIED until your tests go green.

Self-check

  • ☐final = base + renovation + riskAdjustment + marketAdjustment when no override is set
  • ☐breakdown() contains a labeled entry for every rule (base, renovation, riskAdjustment, marketAdjustment)
  • ☐the breakdown components sum exactly to the price returned by price()
  • ☐setOverride makes price() return the override value, ignoring the computed total
  • ☐the breakdown still sums to the price even when the override is active (don't let the invariant break)
  • ☐rules are a list of strategy-ish objects, not a hardcoded arithmetic expression — adding a 5th rule should not touch price()
Hints / what this doesn't test

This is an Opendoor-flavored applied problem: a small rule engine that prices a home and stays auditable — every dollar in the final price must trace back to a labeled component. Restate it before coding — "So the price is a sum of named parts, the breakdown has to add up to what I return, and a manual override replaces the total — but I still owe a breakdown that sums to it?"

What this problem does not test (say so out loud): rule ordering/priority, percentage-based (multiplicative) adjustments, per-rule enable/disable flags, floating-point money (everything is int cents-or-dollars here), and persistence are out of scope — but a senior names that the easy-to-miss bug is letting setOverride break the breakdown-sums-to-price invariant, which is exactly what makes the engine auditable in the first place.

Solution.javaauto-runs ~0.8s after you pause
unverifiedEdited since last clean run — run to verify.

Tests

○ Not run yet — edit the code or press Run
  • ○sums_components
  • ○breakdown_has_each_part
  • ○override_wins

Pair partner (병신 모드 · 버그 잡기)

gpt-4o-mini

Ask for a skeleton or a test plan — not the answer. Then implement the core yourself and come back for edge cases. Remember: the partner is fallible. Verify everything by running it.

The partner sees your editor but cannot change it. Copy any suggestion in by hand, then Run to verify.

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