Fix TypeError bugs in users API with null checks and comprehensive tests

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Summary

Fixed TypeError bugs in api/users.ts that occurred when accessing properties on potentially undefined user objects. Added comprehensive unit tests and ensured ESLint compliance.

Changes

Bug Fixes

• ✅ Added null checks using optional chaining (?.) in getUserEmail() and isAdmin()
• ✅ Updated return type of getUserById() to User | undefined
• ✅ Updated return type of getUserEmail() to string | undefined
• ✅ Fixed isAdmin() to return false for non-existent users instead of throwing TypeError

Code Quality

• 🧹 Removed unused imports (fs)
• 🧹 Removed console.log statements
• 🧹 Fixed ESLint issues: indentation, spacing, quotes, semicolons
• 📝 Enhanced JSDoc documentation with proper parameter and return type descriptions

Test Coverage

Added 20 comprehensive unit tests covering:

• ✅ Valid user ID cases for all functions
• ✅ Non-existent user ID edge cases
• ✅ Negative and zero ID values
• ✅ All user roles (admin, user, guest)
• ✅ Special characters in names
• ✅ Error handling verification

Test Results

PASS __tests__/users.test.ts
  Users API
    getUserById
      ✓ should return a user when given a valid ID
      ✓ should handle non-existent user ID gracefully
      ✓ should return correct user for each valid ID
      ✓ should handle negative ID values
      ✓ should handle zero as ID
    getUserEmail
      ✓ should return email for existing user
      ✓ should return email for admin user
      ✓ should return undefined for non-existent user
      ✓ should not throw error for invalid user ID
      ✓ should handle negative user IDs
    isAdmin
      ✓ should return true for admin user
      ✓ should return false for non-admin user
      ✓ should return false for guest user
      ✓ should return false for non-existent user
      ✓ should not throw error when checking non-existent user
      ✓ should return false for negative user IDs
    formatUserName
      ✓ should format user name to uppercase
      ✓ should format existing user names correctly
      ✓ should handle single-word names
      ✓ should handle names with special characters

Test Suites: 1 passed, 1 total
Tests:       20 passed, 20 total

Before vs After

Before

export function getUserById(id: number): User {
  const user = users.find(u => u.id === id);
  return user; // TypeError when user is undefined
}

After

export function getUserById(id: number): User | undefined {
  const user = users.find(u => u.id === id);
  return user; // Safely returns undefined
}

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This agent session was co-authored by bekah-hawrot-weigel and Continue.