Improve test coverage from 1.18% to 89.21%

- Add comprehensive test suite for api.ts service layer
- Create component tests for BackToTop, ColorCell, MaterialBadge
- Add tests for data modules: bambuLabColors and bambuLabColorsComplete
- Include specialized tests for UI features, CRUD operations, and data consistency
- Achieve 100% coverage for core components and data utilities
- All 91 tests passing with robust mocking strategies

__tests__/components/BackToTop.test.tsx

@@ -0,0 +1,148 @@
+import React from 'react';
+import { render, fireEvent, act } from '@testing-library/react';
+import { BackToTop } from '@/src/components/BackToTop';
+
+// Mock window properties
+global.scrollTo = jest.fn();
+Object.defineProperty(window, 'pageYOffset', {
+  writable: true,
+  configurable: true,
+  value: 0,
+});
+
+describe('BackToTop', () => {
+  beforeEach(() => {
+    jest.clearAllMocks();
+    window.pageYOffset = 0;
+  });
+
+  it('does not render button when at top of page', () => {
+    const { container } = render(<BackToTop />);
+    const button = container.querySelector('button');
+    expect(button).not.toBeInTheDocument();
+  });
+
+  it('renders button when scrolled down', () => {
+    const { container } = render(<BackToTop />);
+    
+    // Simulate scroll down
+    act(() => {
+      window.pageYOffset = 400;
+      fireEvent.scroll(window);
+    });
+    
+    const button = container.querySelector('button');
+    expect(button).toBeInTheDocument();
+  });
+
+  it('hides button when scrolled back up', () => {
+    const { container } = render(<BackToTop />);
+    
+    // Scroll down first
+    act(() => {
+      window.pageYOffset = 400;
+      fireEvent.scroll(window);
+    });
+    
+    expect(container.querySelector('button')).toBeInTheDocument();
+    
+    // Scroll back up
+    act(() => {
+      window.pageYOffset = 100;
+      fireEvent.scroll(window);
+    });
+    
+    expect(container.querySelector('button')).not.toBeInTheDocument();
+  });
+
+  it('scrolls to top when clicked', () => {
+    const { container } = render(<BackToTop />);
+    
+    // Make button visible
+    act(() => {
+      window.pageYOffset = 400;
+      fireEvent.scroll(window);
+    });
+    
+    const button = container.querySelector('button');
+    fireEvent.click(button!);
+    
+    expect(global.scrollTo).toHaveBeenCalledWith({
+      top: 0,
+      behavior: 'smooth'
+    });
+  });
+
+  it('has correct styling when visible', () => {
+    const { container } = render(<BackToTop />);
+    
+    // Make button visible
+    act(() => {
+      window.pageYOffset = 400;
+      fireEvent.scroll(window);
+    });
+    
+    const button = container.querySelector('button');
+    
+    expect(button).toHaveClass('fixed');
+    expect(button).toHaveClass('bottom-8');
+    expect(button).toHaveClass('right-8');
+    expect(button).toHaveClass('bg-blue-600');
+    expect(button).toHaveClass('text-white');
+    expect(button).toHaveClass('rounded-full');
+    expect(button).toHaveClass('shadow-lg');
+  });
+
+  it('has hover effect', () => {
+    const { container } = render(<BackToTop />);
+    
+    // Make button visible
+    act(() => {
+      window.pageYOffset = 400;
+      fireEvent.scroll(window);
+    });
+    
+    const button = container.querySelector('button');
+    expect(button).toHaveClass('hover:bg-blue-700');
+    expect(button).toHaveClass('hover:scale-110');
+  });
+
+  it('contains arrow icon', () => {
+    const { container } = render(<BackToTop />);
+    
+    // Make button visible
+    act(() => {
+      window.pageYOffset = 400;
+      fireEvent.scroll(window);
+    });
+    
+    const svg = container.querySelector('svg');
+    
+    expect(svg).toBeInTheDocument();
+    expect(svg).toHaveClass('w-6');
+    expect(svg).toHaveClass('h-6');
+  });
+
+  it('has aria-label for accessibility', () => {
+    const { container } = render(<BackToTop />);
+    
+    // Make button visible
+    act(() => {
+      window.pageYOffset = 400;
+      fireEvent.scroll(window);
+    });
+    
+    const button = container.querySelector('button');
+    expect(button).toHaveAttribute('aria-label', 'Back to top');
+  });
+
+  it('cleans up scroll listener on unmount', () => {
+    const removeEventListenerSpy = jest.spyOn(window, 'removeEventListener');
+    const { unmount } = render(<BackToTop />);
+    
+    unmount();
+    
+    expect(removeEventListenerSpy).toHaveBeenCalledWith('scroll', expect.any(Function));
+    removeEventListenerSpy.mockRestore();
+  });
+});