Consider proptest and libfuzzer for testing contracts

[hashedone]

I think it would benefit on fuzztest and property test of contracts.

The fuzztests addresses the issue, that when contract crashes, the error message turns out not being nice. Detecting potential crashes early and having example how to integrate those to new contracts, so it would be easier to handle this kind of ptoblems.

Proptest is just a way to slightly generalize tests to easier find bugs in edge cases,

[ethanfrey]

Once we have good unit test setup (pretty good now) and complete multi-test coverage (on our way to do that), I think some automated test tooling would be a good place to invest time.

I like proptest/quicktest style checks. We can just focus on manually testing the business logic for "good" and "fail" cases, and let these automated tools try to find some edge case we missed. It would be great to try this out on a contract and find some best practices and add some docs on how to do so.

[ethanfrey]

Let's at least investigate this as part of v0.12 while adding some code coverage to the CI #172

We can always punt it to v0.13 or later, but adding to the milestone so we investigate it a bit.