fiatcode
3d94c96ed2
- Password Validator kata with starter code and tests - Shopping Cart kata with starter code and tests - FizzBuzz reference code (from live demo) - Setup guide and TDD reference card - No solutions included (participants implement themselves)
62 lines
1.9 KiB
Markdown
62 lines
1.9 KiB
Markdown
# Feature B — Shopping Cart
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## Your goal
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Implement `ShoppingCart` using strict TDD. **Do not write any production code before you have a failing test.**
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## Domain rules to implement (in order)
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| Step | Feature | Notes |
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|------|---------|-------|
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| 1 | Empty cart has subtotal 0 and count 0 | The baseline |
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| 2 | Add items — subtotal = price × quantity | Multiple items accumulate |
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| 3 | Remove item by name | Removing unknown name does nothing |
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| 4 | Apply % discount to subtotal | 10% off $50 → $45 |
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| 5 | CartItem rejects zero/negative price & quantity | Value Object validation |
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| 6 | Bonus: duplicate name / float precision | Design decision — your call |
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## The rhythm — repeat for every rule
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```
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1. Uncomment the next test → run → watch it FAIL (Red)
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2. Write the minimum code to make it pass → run → GREEN
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3. Refactor if needed → run → still GREEN
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4. Move to the next test
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```
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## Running the tests
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```bash
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dart pub get
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dart test
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```
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## Files
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- `lib/shopping_cart.dart` — your implementation goes here
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- `test/shopping_cart_test.dart` — uncomment tests one at a time
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## Design hints (don't peek until you're stuck!)
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<details>
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<summary>Hint for Step 3 — Remove by name</summary>
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When you need to remove by name, a `List<CartItem>` forces you to search by name.
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A `Map<String, CartItem>` makes lookup O(1) and removal trivial.
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Let the test drive you toward the right data structure.
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</details>
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<details>
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<summary>Hint for Step 5 — Value Object</summary>
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Validation belongs in `CartItem`'s constructor, not in `ShoppingCart.addItem()`.
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If the item can't be created, the cart never sees it.
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This is the Value Object pattern: invalid state is unrepresentable.
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</details>
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<details>
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<summary>Hint for the float precision bonus test</summary>
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Use `closeTo(expected, delta)` instead of `equals()` for floating point comparisons.
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Example: `expect(result, closeTo(0.30, 0.001))`
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</details>
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