diff --git a/ecommerce_app/lib/src/features/cart/domain/cart.dart b/ecommerce_app/lib/src/features/cart/domain/cart.dart
index a1999bf9..1fa65068 100644
--- a/ecommerce_app/lib/src/features/cart/domain/cart.dart
+++ b/ecommerce_app/lib/src/features/cart/domain/cart.dart
@@ -1,5 +1,7 @@
 import 'dart:convert';
 
+import 'package:flutter/foundation.dart';
+
 import 'package:ecommerce_app/src/features/cart/domain/item.dart';
 import 'package:ecommerce_app/src/features/products/domain/product.dart';
 
@@ -30,6 +32,16 @@ class Cart {
 
   @override
   String toString() => 'Cart(items: $items)';
+
+  @override
+  bool operator ==(Object other) {
+    if (identical(this, other)) return true;
+
+    return other is Cart && mapEquals(other.items, items);
+  }
+
+  @override
+  int get hashCode => items.hashCode;
 }
 
 extension CartItems on Cart {
diff --git a/ecommerce_app/test/src/features/cart/application/cart_service_test.dart b/ecommerce_app/test/src/features/cart/application/cart_service_test.dart
index e90f112b..eee0b058 100644
--- a/ecommerce_app/test/src/features/cart/application/cart_service_test.dart
+++ b/ecommerce_app/test/src/features/cart/application/cart_service_test.dart
@@ -1,13 +1,22 @@
 import 'package:ecommerce_app/src/features/authentication/data/fake_auth_repository.dart';
+import 'package:ecommerce_app/src/features/authentication/domain/app_user.dart';
 import 'package:ecommerce_app/src/features/cart/application/cart_service.dart';
 import 'package:ecommerce_app/src/features/cart/data/local/local_cart_repository.dart';
 import 'package:ecommerce_app/src/features/cart/data/remote/remote_cart_repository.dart';
+import 'package:ecommerce_app/src/features/cart/domain/cart.dart';
+import 'package:ecommerce_app/src/features/cart/domain/item.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 import 'package:flutter_test/flutter_test.dart';
+import 'package:mocktail/mocktail.dart';
 
 import '../../../mocks.dart';
 
 void main() {
+  setUpAll(() {
+    registerFallbackValue(const Cart());
+  });
+  const testUser = AppUser(uid: 'abc');
+
   late MockAuthRepository authRepository;
   late MockRemoteCartRepository remoteCartRepository;
   late MockLocalCartRepository localCartRepository;
@@ -16,6 +25,7 @@ void main() {
     remoteCartRepository = MockRemoteCartRepository();
     localCartRepository = MockLocalCartRepository();
   });
+
   CartService makeCartService() {
     final container = ProviderContainer(
       overrides: [
@@ -30,11 +40,150 @@ void main() {
 
   group('setItem', () {
     test('null user, writes item to local cart', () async {
+      // setup
+      const expectedCart = Cart({'123': 1});
+      when(() => authRepository.currentUser).thenReturn(null);
+      when(localCartRepository.fetchCart).thenAnswer(
+        (_) => Future.value(const Cart()),
+      );
+      when(() => localCartRepository.setCart(expectedCart)).thenAnswer(
+        (_) => Future.value(),
+      );
       final cartService = makeCartService();
+      // run
+      await cartService.setItem(
+        const Item(productId: '123', quantity: 1),
+      );
+      // verify
+      verify(
+        () => localCartRepository.setCart(expectedCart),
+      ).called(1);
+      verifyNever(
+        () => remoteCartRepository.setCart(any(), any()),
+      );
     });
 
     test('non-null user, writes item to remote cart', () async {
-      // TODO: Implement
+      // setup
+      const expectedCart = Cart({'123': 1});
+      when(() => authRepository.currentUser).thenReturn(testUser);
+      when(() => remoteCartRepository.fetchCart(testUser.uid)).thenAnswer(
+        (_) => Future.value(const Cart()),
+      );
+      when(() => remoteCartRepository.setCart(testUser.uid, expectedCart))
+          .thenAnswer(
+        (_) => Future.value(),
+      );
+      final cartService = makeCartService();
+      // run
+      await cartService.setItem(
+        const Item(productId: '123', quantity: 1),
+      );
+      // verify
+      verify(
+        () => remoteCartRepository.setCart(testUser.uid, expectedCart),
+      ).called(1);
+      verifyNever(
+        () => localCartRepository.setCart(any()),
+      );
+    });
+  });
+
+  group('addItem', () {
+    test('null user, adds item to local cart', () async {
+      // setup
+      const initialCart = Cart({'123': 2});
+      const expectedCart = Cart({'123': 3});
+      when(() => authRepository.currentUser).thenReturn(null); // null user
+      when(localCartRepository.fetchCart).thenAnswer(
+        (_) => Future.value(initialCart), // empty cart
+      );
+      when(() => localCartRepository.setCart(expectedCart)).thenAnswer(
+        (_) => Future.value(),
+      );
+      final cartService = makeCartService();
+      // run
+      await cartService.addItem(const Item(productId: '123', quantity: 1));
+      // verify
+      verify(
+        () => localCartRepository.setCart(expectedCart),
+      ).called(1);
+      verifyNever(
+        () => remoteCartRepository.setCart(any(), any()),
+      );
+    });
+
+    test('non-null user, adds item to remote cart', () async {
+      // setup
+      const initialCart = Cart({'123': 2});
+      const expectedCart = Cart({'123': 3});
+      when(() => authRepository.currentUser).thenReturn(testUser); // null user
+      when(() => remoteCartRepository.fetchCart(testUser.uid)).thenAnswer(
+        (_) => Future.value(initialCart), // empty cart
+      );
+      when(() => remoteCartRepository.setCart(testUser.uid, expectedCart))
+          .thenAnswer(
+        (_) => Future.value(),
+      );
+      final cartService = makeCartService();
+      // run
+      await cartService.addItem(const Item(productId: '123', quantity: 1));
+      // verify
+      verifyNever(
+        () => localCartRepository.setCart(any()),
+      );
+      verify(
+        () => remoteCartRepository.setCart(testUser.uid, expectedCart),
+      ).called(1);
+    });
+  });
+
+  group('removeItem', () {
+    test('null user, removes item from local cart', () async {
+      // setup
+      const initialCart = Cart({'123': 3, '456': 1});
+      const expectedCart = Cart({'456': 1});
+      when(() => authRepository.currentUser).thenReturn(null); // null user
+      when(localCartRepository.fetchCart).thenAnswer(
+        (_) => Future.value(initialCart), // empty cart
+      );
+      when(() => localCartRepository.setCart(expectedCart)).thenAnswer(
+        (_) => Future.value(),
+      );
+      final cartService = makeCartService();
+      // run
+      await cartService.removeItemById('123');
+      // verify
+      verify(
+        () => localCartRepository.setCart(expectedCart),
+      ).called(1);
+      verifyNever(
+        () => remoteCartRepository.setCart(any(), any()),
+      );
+    });
+
+    test('non-null user, removes item from remote cart', () async {
+      // setup
+      const initialCart = Cart({'123': 3, '456': 1});
+      const expectedCart = Cart({'456': 1});
+      when(() => authRepository.currentUser).thenReturn(testUser); // null user
+      when(() => remoteCartRepository.fetchCart(testUser.uid)).thenAnswer(
+        (_) => Future.value(initialCart), // empty cart
+      );
+      when(() => remoteCartRepository.setCart(testUser.uid, expectedCart))
+          .thenAnswer(
+        (_) => Future.value(),
+      );
+      final cartService = makeCartService();
+      // run
+      await cartService.removeItemById('123');
+      // verify
+      verifyNever(
+        () => localCartRepository.setCart(any()),
+      );
+      verify(
+        () => remoteCartRepository.setCart(testUser.uid, expectedCart),
+      ).called(1);
     });
   });
 }