Struct Counterexample

pub struct Counterexample<'a> {
    pub value: PlutusData,
    pub choices: Vec<u8>,
    pub cache: Cache<'a, PlutusData>,
}

—– Counterexample —————————————————————–

A counterexample is constructed from a test failure. It holds a value, and a sequence of random choices that led to this value. It holds a reference to the underlying property and fuzzer. In many cases, a counterexample can be simplified (a.k.a “shrinked”) into a smaller counterexample.

Fields

value: PlutusData

choices: Vec<u8>

cache: Cache<'a, PlutusData>

Implementations

impl Counterexample<'_>

pub fn simplify(&mut self)

Try to simplify a ‘Counterexample’ by manipulating the random sequence of generated values (a.k.a. choices). While the implementation is quite involved, the strategy is rather simple at least conceptually:

Each time a (seeded) fuzzer generates a new value and a new seed, it also stores the generated value in a vector, which we call ‘choices’. If we re-run the test case with this exact choice sequence, we end up with the exact same outcome.

But, we can tweak chunks of this sequence in hope to generate a smaller sequence, thus generally resulting in a smaller counterexample. Each transformations is applied on chunks of size 8, 4, 2 and 1; until we no longer make progress (i.e. hit a fix point).

As per MiniThesis, we consider the following transformations:

• Deleting chunks
• Transforming chunks into sequence of zeroes
• Replacing chunks of values with smaller values
• Sorting chunks in ascending order
• Swapping nearby pairs
• Redistributing values between nearby pairs