Initial commit: TDD Workshop exercises for participants

- 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)

shopping_cart/README.md

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+# 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
+
+```bash
+dart pub get
+dart test
+```
+
+## Files
+
+- `lib/shopping_cart.dart` — your implementation goes here
+- `test/shopping_cart_test.dart` — uncomment tests one at a time
+
+## Design hints (don't peek until you're stuck!)
+
+<details>
+<summary>Hint for Step 3 — Remove by name</summary>
+
+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.
+</details>
+
+<details>
+<summary>Hint for Step 5 — Value Object</summary>
+
+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.
+</details>
+
+<details>
+<summary>Hint for the float precision bonus test</summary>
+
+Use `closeTo(expected, delta)` instead of `equals()` for floating point comparisons.
+Example: `expect(result, closeTo(0.30, 0.001))`
+</details>

shopping_cart/lib/shopping_cart.dart

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+// TODO: Implement ShoppingCart using TDD.
+//
+// Domain rules (implement one at a time, test first!):
+//   1. Add an item (name, price, quantity) to the cart
+//   2. Get the subtotal (sum of price × quantity for all items)
+//   3. Remove an item by name
+//   4. Get total item count (sum of all quantities)
+//   5. Apply a percentage discount to the subtotal (e.g. 10% off)
+//   6. Items with zero or negative price are rejected
+//
+// CartItem is a Value Object — immutable, validated at construction.
+// ShoppingCart is stateful — it accumulates items across calls.
+
+class CartItem {
+  final String name;
+  final double price;
+  final int quantity;
+
+  CartItem({required this.name, required this.price, required this.quantity}) {
+    // TODO: validate price > 0 and quantity > 0
+  }
+}
+
+class ShoppingCart {
+  // TODO: implement
+
+  void addItem(CartItem item) {
+    throw UnimplementedError();
+  }
+
+  void removeItem(String name) {
+    throw UnimplementedError();
+  }
+
+  double subtotal() {
+    throw UnimplementedError();
+  }
+
+  int itemCount() {
+    throw UnimplementedError();
+  }
+
+  double totalAfterDiscount(double discountPercent) {
+    throw UnimplementedError();
+  }
+}

shopping_cart/pubspec.yaml

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+name: shopping_cart
+description: TDD Workshop - Feature B
+
+environment:
+  sdk: ^3.0.0
+
+dev_dependencies:
+  test: ^1.25.0

shopping_cart/test/shopping_cart_test.dart

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+import 'package:test/test.dart';
+import '../lib/shopping_cart.dart';
+
+// ============================================================
+//  SHOPPING CART — Workshop Starter
+//  Follow Red → Green → Refactor strictly.
+//  Uncomment one test at a time. Make it pass. Then the next.
+// ============================================================
+
+void main() {
+  late ShoppingCart cart;
+
+  setUp(() {
+    cart = ShoppingCart();
+  });
+
+  // ──────────────────────────────────────────────────────────
+  // STEP 1 — Empty cart
+  // Before adding anything, the cart should be empty.
+  // Trivial, but sets the baseline. Always start here.
+  // ──────────────────────────────────────────────────────────
+  group('Empty cart', () {
+    test('subtotal is zero when cart is empty', () {
+      // TODO: uncomment when ready
+      // expect(cart.subtotal(), equals(0.0));
+    });
+
+    test('item count is zero when cart is empty', () {
+      // TODO: uncomment when ready
+      // expect(cart.itemCount(), equals(0));
+    });
+  });
+
+  // ──────────────────────────────────────────────────────────
+  // STEP 2 — Adding items
+  // A single item: subtotal = price × quantity.
+  // ──────────────────────────────────────────────────────────
+  group('Adding items', () {
+    test('subtotal reflects a single item added', () {
+      // TODO: uncomment when ready
+      // cart.addItem(CartItem(name: 'Apple', price: 1.50, quantity: 3));
+      // expect(cart.subtotal(), equals(4.50));
+    });
+
+    test('item count reflects quantity of a single item', () {
+      // TODO: uncomment when ready
+      // cart.addItem(CartItem(name: 'Apple', price: 1.50, quantity: 3));
+      // expect(cart.itemCount(), equals(3));
+    });
+
+    test('subtotal accumulates across multiple different items', () {
+      // TODO: uncomment when ready
+      // cart.addItem(CartItem(name: 'Apple', price: 1.50, quantity: 2));  // 3.00
+      // cart.addItem(CartItem(name: 'Banana', price: 0.75, quantity: 4)); // 3.00
+      // expect(cart.subtotal(), equals(6.00));
+    });
+
+    test('item count sums quantities across multiple items', () {
+      // TODO: uncomment when ready
+      // cart.addItem(CartItem(name: 'Apple', price: 1.50, quantity: 2));
+      // cart.addItem(CartItem(name: 'Banana', price: 0.75, quantity: 4));
+      // expect(cart.itemCount(), equals(6));
+    });
+  });
+
+  // ──────────────────────────────────────────────────────────
+  // STEP 3 — Removing items
+  // Removing an item by name should drop it from the subtotal.
+  // ──────────────────────────────────────────────────────────
+  group('Removing items', () {
+    test('removing an item reduces the subtotal', () {
+      // TODO: uncomment when ready
+      // cart.addItem(CartItem(name: 'Apple', price: 1.50, quantity: 2));
+      // cart.addItem(CartItem(name: 'Banana', price: 0.75, quantity: 4));
+      // cart.removeItem('Apple');
+      // expect(cart.subtotal(), equals(3.00));
+    });
+
+    test('removing an item reduces the item count', () {
+      // TODO: uncomment when ready
+      // cart.addItem(CartItem(name: 'Apple', price: 1.50, quantity: 2));
+      // cart.addItem(CartItem(name: 'Banana', price: 0.75, quantity: 4));
+      // cart.removeItem('Apple');
+      // expect(cart.itemCount(), equals(4));
+    });
+
+    test('removing a non-existent item does nothing', () {
+      // TODO: uncomment when ready
+      // cart.addItem(CartItem(name: 'Apple', price: 1.50, quantity: 2));
+      // cart.removeItem('Orange'); // not in cart
+      // expect(cart.subtotal(), equals(3.00));
+    });
+
+    test('cart is empty after removing the only item', () {
+      // TODO: uncomment when ready
+      // cart.addItem(CartItem(name: 'Apple', price: 1.50, quantity: 2));
+      // cart.removeItem('Apple');
+      // expect(cart.subtotal(), equals(0.0));
+      // expect(cart.itemCount(), equals(0));
+    });
+  });
+
+  // ──────────────────────────────────────────────────────────
+  // STEP 4 — Discount
+  // A percentage discount reduces the subtotal proportionally.
+  // Think: what is 10% off $50.00? → $45.00
+  // ──────────────────────────────────────────────────────────
+  group('Applying a percentage discount', () {
+    test('10% discount reduces subtotal correctly', () {
+      // TODO: uncomment when ready
+      // cart.addItem(CartItem(name: 'Apple', price: 10.00, quantity: 5)); // 50.00
+      // expect(cart.totalAfterDiscount(10), equals(45.00));
+    });
+
+    test('0% discount returns the full subtotal', () {
+      // TODO: uncomment when ready
+      // cart.addItem(CartItem(name: 'Apple', price: 10.00, quantity: 5));
+      // expect(cart.totalAfterDiscount(0), equals(50.00));
+    });
+
+    test('100% discount results in zero total', () {
+      // TODO: uncomment when ready
+      // cart.addItem(CartItem(name: 'Apple', price: 10.00, quantity: 5));
+      // expect(cart.totalAfterDiscount(100), equals(0.0));
+    });
+
+    test('discount on empty cart returns zero', () {
+      // TODO: uncomment when ready
+      // expect(cart.totalAfterDiscount(20), equals(0.0));
+    });
+  });
+
+  // ──────────────────────────────────────────────────────────
+  // STEP 5 — CartItem validation (Value Object)
+  // Invalid items should be rejected at construction time.
+  // This is the "Value Object" pattern: impossible to create bad state.
+  // ──────────────────────────────────────────────────────────
+  group('CartItem validation', () {
+    test('rejects an item with a zero price', () {
+      // TODO: uncomment when ready
+      // expect(
+      //   () => CartItem(name: 'Free thing', price: 0, quantity: 1),
+      //   throwsArgumentError,
+      // );
+    });
+
+    test('rejects an item with a negative price', () {
+      // TODO: uncomment when ready
+      // expect(
+      //   () => CartItem(name: 'Broken item', price: -5.00, quantity: 1),
+      //   throwsArgumentError,
+      // );
+    });
+
+    test('rejects an item with zero quantity', () {
+      // TODO: uncomment when ready
+      // expect(
+      //   () => CartItem(name: 'Apple', price: 1.50, quantity: 0),
+      //   throwsArgumentError,
+      // );
+    });
+  });
+
+  // ──────────────────────────────────────────────────────────
+  // BONUS — Edge cases (if you finish early)
+  // ──────────────────────────────────────────────────────────
+  group('Edge cases', () {
+    test('adding the same item name twice replaces it (or accumulates — you decide!)', () {
+      // TODO: uncomment and decide the behavior, then implement it
+      // Hint: this is a design decision. TDD lets the test define the rule.
+      //
+      // Option A — replace:
+      // cart.addItem(CartItem(name: 'Apple', price: 1.50, quantity: 2));
+      // cart.addItem(CartItem(name: 'Apple', price: 1.50, quantity: 5));
+      // expect(cart.itemCount(), equals(5)); // replaced
+      //
+      // Option B — accumulate:
+      // expect(cart.itemCount(), equals(7)); // stacked
+    });
+
+    test('subtotal handles floating point prices accurately', () {
+      // TODO: uncomment when ready
+      // cart.addItem(CartItem(name: 'Item', price: 0.1, quantity: 3)); // 0.1 + 0.1 + 0.1
+      // expect(cart.subtotal(), closeTo(0.30, 0.001)); // use closeTo for floats!
+    });
+  });
+}