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)
1.9 KiB
1.9 KiB
Feature B — Shopping Cart
Your goal
Implement ShoppingCart using strict TDD. Do not write any production code before you have a failing test.
Domain rules to implement (in order)
| Step | Feature | Notes |
|---|---|---|
| 1 | Empty cart has subtotal 0 and count 0 | The baseline |
| 2 | Add items — subtotal = price × quantity | Multiple items accumulate |
| 3 | Remove item by name | Removing unknown name does nothing |
| 4 | Apply % discount to subtotal | 10% off $50 → $45 |
| 5 | CartItem rejects zero/negative price & quantity | Value Object validation |
| 6 | Bonus: duplicate name / float precision | Design decision — your call |
The rhythm — repeat for every rule
1. Uncomment the next test → run → watch it FAIL (Red)
2. Write the minimum code to make it pass → run → GREEN
3. Refactor if needed → run → still GREEN
4. Move to the next test
Running the tests
dart pub get
dart test
Files
lib/shopping_cart.dart— your implementation goes heretest/shopping_cart_test.dart— uncomment tests one at a time
Design hints (don't peek until you're stuck!)
Hint for Step 3 — Remove by name
When you need to remove by name, a List<CartItem> forces you to search by name.
A Map<String, CartItem> makes lookup O(1) and removal trivial.
Let the test drive you toward the right data structure.
Hint for Step 5 — Value Object
Validation belongs in CartItem's constructor, not in ShoppingCart.addItem().
If the item can't be created, the cart never sees it.
This is the Value Object pattern: invalid state is unrepresentable.
Hint for the float precision bonus test
Use closeTo(expected, delta) instead of equals() for floating point comparisons.
Example: expect(result, closeTo(0.30, 0.001))