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:

• My code follows the style guidelines of this project i.e. Pep8
• 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