Table of Contents

How to reproduce a failure

Every Conjecture failure message includes the seed used to generate the counterexample. Pin it to replay the exact same inputs on every run.

Find the seed in the failure output

Falsifying example after 42 examples (seed: 0xDEADBEEF12345678):
  value = 42

Pin the seed with [Property(Seed = ...)]

[Property(Seed = 0xDEADBEEF12345678)]
public bool My_property(int value) => ...;

The test now runs the same inputs deterministically every time. Debugging, adding logging, and stepping through the property all work with the exact failing case.

Remove the seed once the bug is fixed

After fixing the bug, remove the Seed attribute:

// Remove this line once the bug is fixed:
// [Property(Seed = 0xDEADBEEF12345678)]
[Property]
public bool My_property(int value) => ...;

The property resumes random exploration and will find new counterexamples if the fix is incomplete.

Pin via [ConjectureSettings] (assembly-level)

To fix the seed for all tests during a debugging session:

[assembly: ConjectureSettings(Seed = 0xDEADBEEF12345678)]
Warning

Assembly-level seed pinning makes all tests in the assembly deterministic. Remove it before committing.

See also

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