For each property parameter, junit-quickcheck uses a unique value as a seed for the source of randomness used to generate the parameter’s values. To fix the seed value for a property parameter, use the seed attribute of the @When annotation:

    public class SameValues {
        @Property public void holds(@When(seed = -1L) int i) {
            // ...

You may want to fix the seed when a property fails, so that you can test the property over and over again with the same set of generated values that caused the failure.

junit-quickcheck reports the seed used for a given property parameter by logging it to a SLF4J logger named junit-quickcheck.seed-reporting, at DEBUG level:

Seed for parameter com.your.PropertiesClass.propertyMethod:parameterName is 8007238959251963394

Add an SLF4J binding JAR file to your test class path and logging configuration for your chosen bound library to see the seed log messages.