Test cases required to cover the small cell case

[Cstandardlib]

Describe the Testing Issue

Fix for #7023 adopts a new approach to Ewald mxr. We should add a test for this.

Additional Context

No response

Task list for Issue attackers (only for developers)

• Understand the testing issue described by the developer.
• Review the specific test case, expected and actual results, and any error messages.
• Identify the root cause of the test failure or issue.
• If a possible solution is suggested, evaluate its feasibility and effectiveness.
• Implement a fix for the test failure or issue, or create a new test case if needed.
• Verify that the fix resolves the testing issue and the test case passes.
• Review and update any relevant documentation, such as test plans or user guides.
• Ensure the testing issue is resolved and close the ticket.
• Share any lessons learned or best practices with the team to prevent similar issues in the future.