testify `{assert|require}` packages seem to be missing `NotErrorAs` methods.

[ndzik]

When using this gem of a library I realized that the assert and require package seem to be missing a convenience function for NotErrorAs(...).

{assert|require}.NotErrorIs(...) does exist so the absence of the error.As equivalent feels weird.

If there is a reason for this, which I do not see, I would love to be enlightened, else I would happily create a PR for this (:

Right now one has to do the following steps to check for this (which kinda breaks the feel IMHO):

var customErr *package.CustomErr
assert.Error(t, err)
assert.False(t, errors.As(err, &customErr))

or similar.

[RmbRT]

Very good insight, this would be very needful!

[ggwpez]

Impressive. Thank you, Sir.