mypy accepts much broader types then the concept I was proposing. Lets take this example:

  def foo(bar: Optional[float]) -> Optional[float]:
      return bar

  def test_foo():
      assert foo(5) == 5

It has 100% code coverage and mypy will accept it.

What I proposed will complain in this case, that you never tested `foo` with `None` or `float` as input parameters and that it never has seen `foo` returning `None` or `float`.

So even with 100% code coverage and mypy not complaining 'type coverage' could give you some hints that a) your tests are not extensive enough or b) your annotated types are too broad