test: add unit test for formatNumberToBalance

[hyperbolic-versor]

Pull Request type

• [ ] Feature
• [ ] Bugfix
• [ ] Refactor
• [ ] Format
• [ ] Documentation
• [X] Testing
• [ ] Other:

Description

add unit test for avail.js, to improve test coverage.

Related Issues

N/A

Testing Performed

add unit test in git flow

Checklist

• [X] I have performed a self-review of my own code.
• [X] The tests pass successfully with cargo test.
• [X] The code was formatted with cargo fmt.
• [X] The code compiles with no new warnings with cargo build --release and cargo build --release --features runtime-benchmarks.
• [X] The code has no new warnings when using cargo clippy.
• [X] If this change affects documented features or needs new documentation, I have created a PR with a documentation update.

[Leouarz]

Thank you for your contribution. However, externals contribution must be discussed in an issue first before drafting a PR. Also, it's not a good practice to construct a big number with BN('' + ...). It's not testing some edge cases.