Add tests to maths/binary_exponentiation.py

[MaximSmolskiy]

Describe your change:

Increase test coverage from

maths/binary_exponentiation.py                                               15     13    13%   9-17, 21-28

to

maths/binary_exponentiation.py                                               15      7    53%   25-32

• Add an algorithm?
• Fix a bug or typo in an existing algorithm?
• Documentation change?

Checklist:

• I have read CONTRIBUTING.md.
• This pull request is all my own work -- I have not plagiarized.
• I know that pull requests will not be merged if they fail the automated tests.
• This PR only changes one algorithm file. To ease review, please open separate PRs for separate algorithms.
• All new Python files are placed inside an existing directory.
• All filenames are in all lowercase characters with no spaces or dashes.
• All functions and variable names follow Python naming conventions.
• All function parameters and return values are annotated with Python type hints.
• All functions have doctests that pass the automated testing.
• All new algorithms have a URL in its comments that points to Wikipedia or other similar explanation.
• If this pull request resolves one or more open issues then the commit message contains Fixes: #{$ISSUE_NO}.

[CaedenPH]

Could you add more tests, at least to this file?

[MaximSmolskiy]

Could you add more tests, at least to this file?

This one test covers all branches (cases), so I think it will be enough

[cclauss]

This one test covers all branches (cases), so I think it will be enough

Does it cover negative numbers, zero, large numbers, floating point numbers, large negative floating point numbers, letters? As discussed in CONTRIBUTING.md, tests should demonstrate how the algorithm works and also how it deals with bad input.

[cclauss]

Please do not open new pull requests in this repo until November 1st. 2022.