[BF] BF should use the mocha testing framework instead of CW's testing framework

[Nik-Sharp]

Is your feature request related to a problem? Please describe.
CW's testing framework is currently used for BF assertions, but CW's testing framework is deprecated in favor of mocha.

Describe the solution you'd like
BF's testing framework should be changed to mocha.

Describe alternatives you've considered
N/A

[kazk]

chai is installed, and I thought it was used already. Once all tests are compatible with Mocha (use describe, it, and chai assertions correctly), I can switch the test framework to Mocha.

I can also add a new BF version and remove CW test framework there, and gradually migrate. If we're adding a new version, I'm open to any improvements to how it works, including breaking changes. We should make any necessary changes to resolve #55.