Add test infrastructure for safe dependency updates

[Copilot]

Add Test Infrastructure for Hex Viewer

• Set up Vitest as the test framework (lightweight, fast, works well with modern JS)
• Add @testing-library/react for React component testing
• Create tests for utility functions in util.js
  • Test ByteSize component
  • Test useObjectURL hook behavior
  • Test useMedia hook behavior
• Create tests for Hex component logic
  • Test HexPairs formatting
  • Test Ascii conversion
  • Test row address formatting
• Add integration tests for App component
  • Test file drop functionality and hex content display
  • Test hex viewer rendering
  • Test ASCII representation
  • Test file close functionality
  • Test postMessage integration for cross-window communication
  • Test download link generation
  • Test empty file handling
  • Test initial state rendering
  • Test drag active state
• Update package.json test script
• Add test configuration (vitest.config.js)
• Run tests to verify they pass (32 tests passing - 23 unit + 9 integration)
• Verify tests catch regression when dependencies are updated
• Update README with test instructions
• Address code review feedback
• Add GitHub workflow to run tests on every PR
• Add TODO comment for future test improvements
• Fix ES module error by adding type: module to package.json
• Rename config files to .cjs for CommonJS compatibility
• Exclude test files from Snowpack build to prevent dependency conflicts
• Add blob.arrayBuffer() polyfill for jsdom compatibility
• Improve test code quality with error handling and helper functions
• Fix CI test failures by switching from jsdom to happy-dom

Original prompt

Add some tests for this project. The goal is to allow me to update dependencies and know that I haven't broken stuff.

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[benfoxall]

@copilot Could you add a github workflow file to run the tests on every pr

[Copilot]

@copilot Could you add a github workflow file to run the tests on every pr

Added in df708ad. The workflow will run tests on every PR and push to main using npm test.

[benfoxall]

@copilot The tests seem to be failing because of a missing package type.

Could you look at the failure and try and correct the error?

[Copilot]

@copilot The tests seem to be failing because of a missing package type.

Could you look at the failure and try and correct the error?

Fixed in 73567a7. The issue was that Vite/Vitest v7.x are ES modules only and require "type": "module" in package.json. Tests now pass successfully.

[benfoxall]

@copilot I think this is missing some higher level tests – like "can I drop a file in the window and see the hex contents of it"

[Copilot]

@copilot I think this is missing some higher level tests – like "can I drop a file in the window and see the hex contents of it"

Added in 5af714c. Created 9 integration tests in App.test.jsx that test the complete user workflow:

• File drop functionality
• Hex content rendering after file drop
• ASCII representation display
• File close functionality
• PostMessage integration
• Download link functionality
• Empty file handling

All 32 tests now pass (23 unit tests + 9 integration tests).

[benfoxall]

[benfoxall]

@copilot looks like the tests are failing 🤔

[Copilot]

@copilot looks like the tests are failing 🤔

Fixed in 5e5c410. The issue was that jsdom v27.x has a dependency (@exodus/bytes) that's an ES module, which conflicts with the "type": "module" setting in package.json. Switched to happy-dom which is fully compatible with ES modules. All 32 tests now pass in CI.