CSUB-347: Follow up on tests

[atodorov]

Description of proposed changes:

Practical tips for PR review & merge:

• All GitHub Actions report PASS
• Newly added code/functions have unit tests
  • Coverage tools report all newly added lines as covered
  • The positive scenario is exercised
  • Negative scenarios are exercised, e.g. assert on all possible errors
  • Assert on events triggered if applicable
  • Assert on changes made to storage if applicable
• Modified behavior/functions - try to make sure above test items are covered
• Integration tests are added if applicable/needed

[atodorov]

@CAGS295 for sortition::threshold() can you explain to me what the expected behavior should be so that we can encode it via property based test(s) ?

[github-actions]

For full LLVM coverage report click here!

[CAGS295]

Same properties as model. Threshold is a model analogous with u128 as output instead of a floating point [0,1]. threshold is model(..).mul(u128::MAX) so the output is within [0,u128::MAX]. I'm curious what is the precision error when you try to

let {n,d} = bigrational::from(f64::epsilon);
x = model(..);
x / d * n

The question is, what is the geometric difference between the true value and actual output. and if f64::epsilon is an achievable output from model in the first place.
Another interesting test would be bigrational::from(1 - f64::epsilon)