Store and diff output from explain() as part of test suite #242
Description
When making a PR like github.com//pull/241 focused on changing how the output error messages appear to the user, it seems tricky to review without manually running .
Since part of the purpose of check-datapackage is to generate human readable error messages, I wonder if we should include in the test suite how these error messages will change after a new PR is merged. This is commonly done for visualization libraries since it is not easy to infer which changes to the output could come about from certain code changes.
Here, we could do something similar by storing/committing the output of explain() on all the test cases and then automatically updating it as part of the test suite. Then you would see on each PR if any changes were introduced to how the explain() messages would look for the various tests instead of trying to infer it for the code changes.