[request] Unit test suite

[timothyliu3d]

I wish there is a unit test suite so we can:

• run tests locally when developing/contributing
• auto-run tests upon PR creation, this requires CI
• have regression tests to maintain existing expectations when adding/updating features
• have Maya version-specific and OS-specific tests
• etc

[miquelcampos]

@timothyliu3d
I tried in the past, but it was too much work since the code base is now very big.
Sadly my time is limited and can't dedicate the time to create tests for everything.
But I will consider it if I get help from volunteers