Client

A comprehensive shopping list application demonstrating React best practices and 96.63% test coverage through modern testing methodologies.

ShoppingList - uitgebreide boodschappenlijst applicatie

Project Overview

This shopping list application represents a deep dive into modern React development, emphasizing test-driven development and production-ready code quality. Built from the ground up with testing as a first-class citizen, the project demonstrates how comprehensive testing strategies lead to maintainable, robust applications.

The application allows users to organize their shopping by supermarket, categorize items by store sections (Produce, Dairy, Bakery), and manage their lists with an intuitive dark-themed interface. But beyond the features, this project showcases a professional approach to React development with enterprise-level testing practices.

🎯 Success Metrics

A successful React application means:

96.63% test coverage across unit, integration, and E2E tests
Type-safe codebase with TypeScript throughout
Comprehensive test suite with React Testing Library and Playwright
Production-ready code architecture and patterns
Accessible, responsive UI that works across all devices

Testing Excellence

Test coverage rapport met 96.63% totale dekking en gedetailleerde breakdown per component

The Testing Philosophy

This project was built with a test-first mindset, where every feature began with test cases that defined expected behavior. Using React Testing Library, I focused on testing user interactions rather than implementation details, ensuring tests remain stable through refactoring.

The testing pyramid includes:

Unit tests for hooks, utilities, and isolated components
Integration tests for component interactions and state management
E2E tests with Playwright for critical user journeys
Accessibility tests ensuring WCAG compliance

This multi-layered approach catches bugs at different levels while maintaining fast feedback loops during development.

React Architecture

Development Process

Test-Driven Development

Every feature followed a TDD workflow:

Write failing tests that define expected behavior
Implement minimal code to pass tests
Refactor while keeping tests green
Verify coverage and add edge case tests

This approach resulted in 96.63% coverage with meaningful, maintainable tests that actually catch regressions.

Component Architecture

Built modular, reusable components with clear responsibilities
Implemented composition patterns for flexibility
Created custom hooks for shared logic (useLocalStorage, useShoppingList)
Established consistent props interfaces with TypeScript

State Management Strategy

Chose Context API for its simplicity and testability:

Centralized state in ShoppingListContext with reducer pattern
Created custom hook (useShoppingList) for type-safe context consumption
Implemented localStorage persistence through custom useLocalStorage hook
Made context fully testable with comprehensive test suite

React Testing Library Approach

Testing focused on user behavior rather than implementation:

Used semantic queries (getByRole, getByLabelText) for accessible tests
Tested user interactions with @testing-library/user-event
Created custom render utilities with providers for consistent setup
Avoided testing implementation details (state, internal functions)
Verified accessibility with proper ARIA attributes and roles

Test Coverage Breakdown

Gedetailleerde test coverage per component met hoge dekking over alle modules

Testing Strategy Deep Dive

This project showcases a comprehensive testing strategy that ensures reliability, maintainability, and confidence in every code change.

Unit Testing with Vitest

Lightning-fast unit tests for isolated logic:

Custom hooks tested in isolation with renderHook
Context providers tested with mock consumers
Utility functions tested with edge cases
100% coverage on critical business logic

Integration Testing

React Testing Library for component interactions:

User event simulations (click, type, keyboard navigation)
Form submissions and validation flows
Modal interactions and state changes
Filter and search functionality

E2E Testing with Playwright

Full user journey testing across browsers:

Complete user flows from onboarding to task completion
localStorage persistence verification across page reloads
Cross-browser compatibility testing
Accessibility testing with axe-core integration

Key Testing Achievements

96.63% Code Coverage

Comprehensive coverage across all layers:

Components: 100% coverage on critical UI components (ItemCard, SupermarketManager, etc.)
Context & Hooks: 100% coverage on state management and custom hooks
Pages: 83.57% coverage with E2E tests filling the gaps
Coverage reports: HTML reports with line-by-line analysis using Vitest coverage

Test Quality Metrics

Zero flaky tests: Deterministic test suite with proper async handling
Fast feedback: Unit tests run in less than 1 second, full suite in less than 10 seconds
Maintainable tests: Tests using user-centric queries remain stable through refactoring
CI-ready: Tests configured for automated pipelines with coverage thresholds

React Best Practices

This project demonstrates production-ready React patterns:

Performance Optimization

Memoization with useMemo and useCallback where appropriate
Code splitting and lazy loading for optimal bundle size
Efficient re-render prevention through proper prop design
localStorage throttling to prevent excessive writes

Accessibility First

Semantic HTML with proper heading hierarchy
ARIA labels and roles for screen reader compatibility
Keyboard navigation (Tab, Enter, Escape) throughout
Focus management in modals and dynamic content
Color contrast meeting WCAG AA standards

TypeScript Integration

Strict mode enabled for maximum type safety
Comprehensive interface definitions for all data models
Generic types for reusable components and hooks
Zero ‘any’ types in production code

Results

Project Outcomes

96.63%

Test Coverage

100%

TypeScript Coverage

40+

Test Suites

Flaky Tests

Technical Learnings

This project reinforced several key principles:

Test-driven development leads to better architecture: Writing tests first forced me to think about component APIs and separation of concerns
React Testing Library’s philosophy works: Testing user behavior instead of implementation details created resilient, maintainable tests
TypeScript catches bugs before runtime: Strict typing prevented numerous potential runtime errors
E2E tests complement unit tests: Playwright caught integration issues that unit tests missed, especially around localStorage persistence
Accessibility from the start is easier: Building with keyboard navigation and screen readers in mind from day one prevented costly retrofitting

What Makes This Project Stand Out

Beyond the features, this project demonstrates:

Production-ready code quality: Not just a prototype, but code ready for real users
Comprehensive testing strategy: Multi-layered testing approach catching issues at every level
Modern React patterns: Hooks, Context API, custom hooks, composition
Developer experience: Clear component APIs, helpful TypeScript types, comprehensive tests
Maintainability focus: Code is easy to understand, modify, and extend

Conclusion

This shopping list application is more than a functional app—it’s a demonstration of React engineering excellence. With 96.63% test coverage, comprehensive E2E testing, and production-ready architecture, it showcases the skills and discipline required for professional React development.

The project proves that thorough testing doesn’t slow development—it accelerates it by catching bugs early, enabling confident refactoring, and creating living documentation through test cases.

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