[proposal] CI should fail if diff coverage is below 70%

[jasonliu747]

Why is this needed:
Diff coverage is the percentage of new or modified lines that are covered by tests. This provides a clear and achievable standard for code review: If you touch a line of code, that line should be covered.

Code coverage is every developer's responsibility!

So, I think CI should fail if diff coverage is below 70% or something else.

Is there a suggested solution, if so, please add it:
Codecov might support this. Need to do some research.

[jasonliu747]

Expect something like this:

[hormes]

+10086

[jasonliu747]

@saintube #131 didn't work, please take a look when you're free. Thanks.