add test for coin change function

[tranlinh19021320]

Description

Please include a summary of the change and which issue is fixed or what question/feature you have added.

Fixes # (issue)

Type of change

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• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature/question
• [ ] This change requires a documentation update
• [ ] Bookmark link

Checklist:

• [x] My code follows the style guidelines of this project i.e. Pep8
• [x] I have performed a self-review of my own code
• [ ] I have commented my code, particularly in hard-to-understand areas
• [ ] I have made corresponding changes to the documentation
• [ ] Any dependent changes have been merged and published in downstream modules
• [ ] I have squashed unnecessary commits

[tranlinh19021320]

Here are Test report https://docs.google.com/document/d/1uiIc8xLfHA-bzDjHew1cjVUWsAF7YkG9FT-a9itDfLk/edit?usp=sharing