Feat: Want to Add test files for atcoder

[Santhosh-Siddhardha]

Describe the feature

Test all the methods of the atcoder module and add a test file.
Will add test file in directory src/test.
Will Check the atcoder.py file as a reference to get an idea about structuring the code.
Will use unittest only.

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• I agree to follow this project's Code of Conduct
• I'm a GSSoC'24 contributor
• I want to work on this issue

[nikhil25803]

Go ahead @Santhosh-Siddhardha

• Add test file in directory src/test.
• Use unittest only.****