Feature request

It would be beneficial to add new rules to the acceptance tests. Currently, two rules are tested:

• Does the validator that uses the new code contribution generate more new errors than allowed?
• Were there too many corrupted sources/datasets during validation?
  Although these rules are fundamental to the acceptance tests, other aspects are not considered: disappearing errors or warnings, unusual info notices, etc.

Is your feature request related to a problem? Please describe.
Specifically in #1188, the acceptance tests passed, even though the initial implementation prevented the validator from checking most of the validation rules. The reports generated did not contain any errors or warnings. Also, the reports contained the unknown_file info notice for required files such as stop_times.txt. Although the acceptance tests were not originally designed to cover this use case, it would be nice if they did.

Proposed solution
First, I think adding two new rules would be helpful:

• Are too many errors disappearing?
• Are too many warnings disappearing?

Another potential additional rule would be

• Do the reports contain the unknown_file notice for the required files?
  since this is an indicator of a problem, but it is very specific.