Modernize action: Node 20, fix vulnerabilities, add tests

[Copilot]

Updated deprecated Node 12 runtime and added test coverage for maintainability.

Changes

Runtime & Dependencies

• Upgraded to Node 20 runtime (Node 12 EOL)
• Updated all dependencies to latest versions, eliminating 14 vulnerabilities (7 high, 6 moderate, 1 low)
• Fixed deprecated yaml.safeLoad() → yaml.load()

Code Refactoring

• Extracted functions to accept parameters instead of module-level globals, enabling testability
• Added module exports for testing without breaking existing behavior

Test Infrastructure

• Added Jest with 17 unit tests covering:
  • Jazzy install command generation with version handling
  • CLI argument construction and config file integration
  • Output directory extraction from args and YAML/JSON configs
  • Priority resolution (args override config, --output over -o)

Example

Before (untestable):

const jazzyArgs = core.getInput("args")
const getDocumentationFolder = () => {
  if (jazzyArgs && jazzyArgs.includes("--output")) {
    return sliceDocumentsFromJazzyArgs("--output")
  }
  return "docs"
}

After (testable):

const getDocumentationFolder = (jazzyArgs, configFilePath) => {
  if (jazzyArgs && jazzyArgs.includes("--output")) {
    return sliceDocumentsFromJazzyArgs(jazzyArgs, "--output")
  }
  return "docs"
}

Rebuilt dist/index.js with updated code. All existing functionality preserved.

Original prompt

Update this and add tests

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