Align JUnit class name example with the Test suffix

[arey]

Ensure that the JUnit class name is aligned with the Test suffix.

Pull Request Checklist

• [ X] I have read and followed the CONTRIBUTING.md guidelines.
• My contribution adds a new instruction, prompt, or chat mode file in the correct directory.
• The file follows the required naming convention.
• The content is clearly structured and follows the example format.
• I have tested my instructions, prompt, or chat mode with GitHub Copilot.
• I have run node update-readme.js and verified that README.md is up to date.

---

Description

The example CalculatorTests was not aligned with the Test (and not Tests suffix).

---

Type of Contribution

• New instruction file.
• New prompt file.
• New chat mode file.
• [ X] Other (please specify): minor / typo

---

By submitting this pull request, I confirm that my contribution abides by the Code of Conduct and will be licensed under the MIT License.

[Copilot]

Pull Request Overview

This PR corrects a minor inconsistency in the JUnit test class naming example by changing CalculatorTests to CalculatorTest to align with the documented Test suffix convention.

• Fixes the example class name to follow the stated naming convention of using singular Test suffix