test: add a test case for appendAdditionalUserAgent in ask-sdk-core

[hideokamoto]

Description

Just add a test case for ask-sdk-core.

Motivation and Context

I check ask-sdk-core's test coverage.

=============================== Coverage summary ===============================
Statements   : 99.78% ( 452/453 )
Branches     : 98.4% ( 246/250 )
Functions    : 96.46% ( 109/113 )
Lines        : 99.77% ( 429/430 )
================================================================================

After adding the test, the Branches will be 100%.

=============================== Coverage summary ===============================
Statements   : 100% ( 453/453 )
Branches     : 100% ( 250/250 )
Functions    : 96.46% ( 109/113 )
Lines        : 100% ( 430/430 )
================================================================================

Testing

Just run a unit test code.

Screenshots (if appropriate)

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)
• [ ] Docs(Add new document content)
• [ ] Translate Docs(Translate document content)
• [x] Test code

Checklist

• [x] My code follows the code style of this project
• [x] My change requires a change to the documentation
• [x] I have updated the documentation accordingly
• [x] I have read the README document
• [x] I have added tests to cover my changes
• [x] All new and existing tests passed
• [x] My commit message follows Conventional Commit Guideline

License

• [x] I confirm that this pull request can be released under the Apache 2 license

[ShenChen93]

Hi @hideokamoto

Thanks for the PR. Merged !