Fix issue 323 prototypes tests

[Felsilva15]

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PR Checklist

• [x] Addresses an existing open issue: fixes #323
• [x] That issue was marked as accepting prs
• [x] Steps in CONTRIBUTING.md were taken

Overview

Add comprehensive test suite for the prototypes-to-classes exercise in the-typeinator project.

This PR adds the missing index.test.js file that was requested in issue #323. The test file includes:

• Conditional test skipping: Tests are skipped when index.js is empty (learner mode), allowing students to start with clean files
• Solution validation: Tests run properly when TEST_SOLUTIONS=true is set (validation mode)
• Comprehensive coverage: Tests for both Robot and Humanoid classes including:
  • Class construction with proper properties
  • Method functionality (announce, charge, move)
  • Inheritance behavior (Humanoid extends Robot)
  • Console output validation with Jest mocks
  • Power management and error handling logic

The implementation follows the same pattern established in other test files in the repository, ensuring consistency with the educational workflow.