Add test case for reverseWordsByCharWithAddtionalStorage method by white box testing

[hoangkimminh]

By submitting this pull request I confirm I've read and complied with the below requirements.

• [x] I have read the Contribution guidelines and I am confident that my PR reflects them.
• [x] I have followed the coding guidelines for this project.
• [x] My code follows the skeleton code structure.
• [x] This pull request has a descriptive title. For example, Added {Algorithm/DS name} [{Language}], not Update README.md or Added new code.

[hoangkimminh]

Steps

• Make the corresponding control flow graph
• Calculate the cyclomatic complexity
• Find the independent paths
• Design test cases corresponding to each independent path