feat: add comprehensive unit tests for DisplayIcon component

- 30+ test cases covering rendering, props, edge cases, and accessibility
- Mock all dependencies and ensure SonarQube compliance
- Test both snake_case and camelCase property conventions

Author: RizWaaN3024

frontend/__tests__/unit/components/DisplayIcon.test.tsx

@@ -0,0 +1,322 @@
+import { render, screen } from '@testing-library/react'
+import userEvent from '@testing-library/user-event'
+import type { Icon } from 'types/icon'
+import DisplayIcon from 'components/DisplayIcon'
+
+jest.mock('@heroui/tooltip', () => ({
+  Tooltip: ({ children, content, delay, closeDelay, showArrow, placement }: never) => (
+    <div
+      data-testid="tooltip"
+      data-tooltip-content={content}
+      data-delay={delay}
+      data-close-delay={closeDelay}
+      data-show-arrow={showArrow}
+      data-placement={placement}
+    >
+      {children}
+    </div>
+  ),
+}))
+
+jest.mock('millify', () => ({
+  millify: jest.fn((value: number, options?: { precision: number }) => {
+    if (value >= 1000000000) return `${(value / 1000000000).toFixed(options?.precision || 1)}B`
+    if (value >= 1000000) return `${(value / 1000000).toFixed(options?.precision || 1)}M`
+    if (value >= 1000) return `${(value / 1000).toFixed(options?.precision || 1)}k`
+    return value.toString()
+  }),
+}))
+
+jest.mock('wrappers/FontAwesomeIconWrapper', () => {
+  return function MockFontAwesomeIconWrapper({ className, icon }: never) {
+    return <span data-testid="font-awesome-icon" data-icon={icon} className={className} />
+  }
+})
+
+jest.mock('utils/data', () => ({
+  ICONS: {
+    starsCount: { label: 'Stars', icon: 'fa-star' },
+    forksCount: { label: 'Forks', icon: 'fa-code-fork' },
+    contributorsCount: { label: 'Contributors', icon: 'fa-users' },
+    contributionCount: { label: 'Contributors', icon: 'fa-users' },
+    issuesCount: { label: 'Issues', icon: 'fa-exclamation-circle' },
+    license: { label: 'License', icon: 'fa-balance-scale' },
+    unknownItem: { label: 'Unknown', icon: 'fa-question' },
+  },
+  iconKeys: 'starsCount' as never,
+}))
+
+describe('DisplayIcon', () => {
+  const mockIcons: Icon = {
+    starsCount: 1250,
+    forksCount: 350,
+    contributorsCount: 25,
+    contributionCount: 25,
+    issuesCount: 42,
+    license: 'MIT',
+  }
+
+  describe('Basic Rendering', () => {
+    it('renders successfully with minimal required props', () => {
+      render(<DisplayIcon item="starsCount" icons={mockIcons} />)
+      expect(screen.getByTestId('tooltip')).toBeInTheDocument()
+    })
+
+    it('renders nothing when item is not in icons object', () => {
+      const { container } = render(<DisplayIcon item="nonexistentItem" icons={mockIcons} />)
+      expect(container.firstChild).toBeNull()
+    })
+
+    it('renders nothing when icons object is empty', () => {
+      const { container } = render(<DisplayIcon item="starsCount" icons={{}} />)
+      expect(container.firstChild).toBeNull()
+    })
+  })
+
+  describe('Conditional Rendering Logic', () => {
+    it('renders when item exists in icons object', () => {
+      render(<DisplayIcon item="starsCount" icons={mockIcons} />)
+      expect(screen.getByTestId('tooltip')).toBeInTheDocument()
+    })
+
+    it('does not render when item does not exist in icons object', () => {
+      const { container } = render(<DisplayIcon item="nonexistent" icons={mockIcons} />)
+      expect(container.firstChild).toBeNull()
+    })
+
+    it('does not render when icons[item] is falsy', () => {
+      const iconsWithFalsy: Icon = { ...mockIcons, starsCount: 0 }
+      const { container } = render(<DisplayIcon item="starsCount" icons={iconsWithFalsy} />)
+      expect(container.firstChild).toBeNull()
+    })
+  })
+
+  describe('Prop-based Behavior', () => {
+    it('displays correct icon based on item prop', () => {
+      render(<DisplayIcon item="starsCount" icons={mockIcons} />)
+      const icon = screen.getByTestId('font-awesome-icon')
+      expect(icon).toHaveAttribute('data-icon', 'fa-star')
+    })
+
+    it('displays different icons for different items', () => {
+      const { rerender } = render(<DisplayIcon item="forksCount" icons={mockIcons} />)
+      expect(screen.getByTestId('font-awesome-icon')).toHaveAttribute('data-icon', 'fa-code-fork')
+
+      rerender(<DisplayIcon item="contributorsCount" icons={mockIcons} />)
+      expect(screen.getByTestId('font-awesome-icon')).toHaveAttribute('data-icon', 'fa-users')
+    })
+
+    it('applies different container classes based on item type', () => {
+      const { rerender, container } = render(<DisplayIcon item="starsCount" icons={mockIcons} />)
+      let containerDiv = container.querySelector('div[class*="rotate-container"]')
+      expect(containerDiv).toBeInTheDocument()
+
+      rerender(<DisplayIcon item="forksCount" icons={mockIcons} />)
+      containerDiv = container.querySelector('div[class*="flip-container"]')
+      expect(containerDiv).toBeInTheDocument()
+    })
+
+    it('applies different icon classes based on item type', () => {
+      const { rerender } = render(<DisplayIcon item="starsCount" icons={mockIcons} />)
+      let icon = screen.getByTestId('font-awesome-icon')
+      expect(icon).toHaveClass('icon-rotate')
+
+      rerender(<DisplayIcon item="forksCount" icons={mockIcons} />)
+      icon = screen.getByTestId('font-awesome-icon')
+      expect(icon).toHaveClass('icon-flip')
+    })
+  })
+
+  describe('Text and Content Rendering', () => {
+    it('displays formatted numbers using millify for numeric values', () => {
+      render(<DisplayIcon item="starsCount" icons={mockIcons} />)
+      expect(screen.getByText('1.3k')).toBeInTheDocument()
+    })
+
+    it('displays string values as-is', () => {
+      render(<DisplayIcon item="license" icons={mockIcons} />)
+      expect(screen.getByText('MIT')).toBeInTheDocument()
+    })
+
+    it('displays tooltip with correct label', () => {
+      render(<DisplayIcon item="starsCount" icons={mockIcons} />)
+      const tooltip = screen.getByTestId('tooltip')
+      expect(tooltip).toHaveAttribute('data-tooltip-content', 'Stars')
+    })
+
+    it('formats large numbers correctly', () => {
+      const largeNumberIcons: Icon = { starsCount: 1500000 }
+      render(<DisplayIcon item="starsCount" icons={largeNumberIcons} />)
+      expect(screen.getByText('1.5M')).toBeInTheDocument()
+    })
+  })
+
+  describe('Default Values and Fallbacks', () => {
+    it('handles items not in ICONS constant gracefully', () => {
+      const testIcons: Icon = { unknownItem: 'test' }
+
+      render(<DisplayIcon item="unknownItem" icons={testIcons} />)
+
+      const tooltip = screen.getByTestId('tooltip')
+      expect(tooltip).toHaveAttribute('data-tooltip-content', 'Unknown')
+    })
+
+    it('applies base classes even without special item types', () => {
+      render(<DisplayIcon item="license" icons={mockIcons} />)
+      const tooltipContainer = screen.getByTestId('tooltip').querySelector('div')
+      expect(tooltipContainer).toHaveClass(
+        'flex',
+        'flex-row-reverse',
+        'items-center',
+        'justify-center'
+      )
+    })
+  })
+
+  describe('Edge Cases and Invalid Inputs', () => {
+    it('throws error when icons object is null', () => {
+      expect(() => {
+        render(<DisplayIcon item="starsCount" icons={null as never} />)
+      }).toThrow('Cannot read properties of null')
+    })
+
+    it('throws error when icons object is undefined', () => {
+      expect(() => {
+        render(<DisplayIcon item="starsCount" icons={undefined as never} />)
+      }).toThrow('Cannot read properties of undefined')
+    })
+
+    it('handles empty string item', () => {
+      const { container } = render(<DisplayIcon item="" icons={mockIcons} />)
+      expect(container.firstChild).toBeNull()
+    })
+
+    it('handles zero values correctly', () => {
+      const zeroIcons: Icon = { starsCount: 0 }
+      const { container } = render(<DisplayIcon item="starsCount" icons={zeroIcons} />)
+      expect(container.firstChild).toBeNull()
+    })
+
+    it('handles negative numbers', () => {
+      const negativeIcons: Icon = { starsCount: -5 }
+      render(<DisplayIcon item="starsCount" icons={negativeIcons} />)
+      expect(screen.getByText('-5')).toBeInTheDocument()
+    })
+
+    it('handles very large numbers', () => {
+      const largeIcons: Icon = { starsCount: 1500000000 }
+      render(<DisplayIcon item="starsCount" icons={largeIcons} />)
+      expect(screen.getByText('1.5B')).toBeInTheDocument()
+    })
+  })
+
+  describe('DOM Structure and Classes', () => {
+    it('has correct base container structure', () => {
+      render(<DisplayIcon item="license" icons={mockIcons} />)
+      const tooltip = screen.getByTestId('tooltip')
+      const containerDiv = tooltip.querySelector('div')
+
+      expect(containerDiv).toHaveClass(
+        'flex',
+        'flex-row-reverse',
+        'items-center',
+        'justify-center',
+        'gap-1',
+        'px-4',
+        'pb-1',
+        '-ml-2'
+      )
+    })
+
+    it('applies rotate-container class for stars items', () => {
+      const { rerender } = render(<DisplayIcon item="starsCount" icons={mockIcons} />)
+      let tooltipContainer = screen.getByTestId('tooltip').querySelector('div')
+      expect(tooltipContainer).toHaveClass('rotate-container')
+
+      rerender(<DisplayIcon item="starsCount" icons={mockIcons} />)
+      tooltipContainer = screen.getByTestId('tooltip').querySelector('div')
+      expect(tooltipContainer).toHaveClass('rotate-container')
+    })
+
+    it('applies flip-container class for forks and contributors items', () => {
+      const testCases = [
+        { item: 'forksCount', value: 100 },
+        { item: 'forksCount', value: 100 },
+        { item: 'contributors_count', value: 50 },
+        { item: 'contributionCount', value: 30 },
+      ]
+
+      testCases.forEach(({ item, value }) => {
+        const iconsWithItem: Icon = { [item]: value }
+        const { container } = render(<DisplayIcon item={item} icons={iconsWithItem} />)
+        const containerDiv = container.querySelector('div[class*="flip-container"]')
+        expect(containerDiv).toBeInTheDocument()
+      })
+    })
+
+    it('applies correct icon classes', () => {
+      render(<DisplayIcon item="starsCount" icons={mockIcons} />)
+      const icon = screen.getByTestId('font-awesome-icon')
+      expect(icon).toHaveClass('text-gray-600', 'dark:text-gray-300', 'icon-rotate')
+    })
+
+    it('applies correct text span classes', () => {
+      render(<DisplayIcon item="license" icons={mockIcons} />)
+      const textSpan = screen.getByText('MIT')
+      expect(textSpan).toHaveClass('text-gray-600', 'dark:text-gray-300')
+    })
+  })
+
+  describe('Accessibility', () => {
+    it('provides tooltip with descriptive content', () => {
+      render(<DisplayIcon item="starsCount" icons={mockIcons} />)
+      const tooltip = screen.getByTestId('tooltip')
+      expect(tooltip).toHaveAttribute('data-tooltip-content', 'Stars')
+    })
+
+    it('has proper tooltip configuration', () => {
+      render(<DisplayIcon item="forksCount" icons={mockIcons} />)
+      const tooltip = screen.getByTestId('tooltip')
+      expect(tooltip).toHaveAttribute('data-delay', '150')
+      expect(tooltip).toHaveAttribute('data-close-delay', '100')
+      expect(tooltip).toHaveAttribute('data-show-arrow', 'true')
+      expect(tooltip).toHaveAttribute('data-placement', 'top')
+    })
+  })
+
+  describe('Internal Logic', () => {
+    it('correctly determines numeric vs string values', () => {
+      const mixedIcons: Icon = {
+        starsCount: 1000,
+        license: 'Apache-2.0',
+      }
+
+      const { rerender } = render(<DisplayIcon item="starsCount" icons={mixedIcons} />)
+      expect(screen.getByText('1.0k')).toBeInTheDocument()
+
+      rerender(<DisplayIcon item="license" icons={mixedIcons} />)
+      expect(screen.getByText('Apache-2.0')).toBeInTheDocument()
+    })
+
+    it('filters and joins className arrays correctly', () => {
+      render(<DisplayIcon item="license" icons={mockIcons} />)
+      const tooltipContainer = screen.getByTestId('tooltip').querySelector('div')
+      const classes = tooltipContainer?.className.split(' ') || []
+
+      expect(classes.filter((cls) => cls === '')).toHaveLength(0)
+    })
+  })
+
+  describe('Event Handling', () => {
+    it('renders tooltip wrapper that can handle hover events', async () => {
+      const user = userEvent.setup()
+      render(<DisplayIcon item="starsCount" icons={mockIcons} />)
+
+      const tooltip = screen.getByTestId('tooltip')
+      expect(tooltip).toBeInTheDocument()
+
+      await user.hover(tooltip)
+      expect(tooltip).toBeInTheDocument()
+    })
+  })
+})