Better testing approach for the generated parser?

[ciaranmcnulty]

Currently we test the parser primarily via the testdata features. These are pretty good as documentation of the correct behaviour in specific situations.

However looking at 'coverage', they cover less than 30% of the Parser's LOC in the PHP version, and probably similar in others.

Is there another approach we can use to validate the Parser is 'correct' in a wide range of situations? I'm thinking

• Fuzz testing?
• Property-based testing?
• Some sort of approvals-based testing?

[mpkorstanje]

Before looking into any of those it might be good to understand why with the existing test set the coverage is so low.

If we are missing examples categorically we may be able to add a few without losing any documentation value (i.e. we won't add trivial examples).