Java Test Data Generator: Datafaker and Instancio for JUnit 5 Test Fixtures

Instancio owns object topology; Datafaker owns vocabulary (names, addresses). With @ExtendWith(InstancioExtension.class), a failing test prints the seed that drove the run. Copy that number into @Seed(n) on the test method to replay the exact failure, then remove the annotation after the fix (Instancio user guide "Reproducing failed tests," retrieved 2026-08-01).

Verified against library docs retrieved 2026-08-01. The second method shows the @Seed replay loop; replace 12345L with the seed printed by InstancioExtension in CI.

// Maven/Gradle coordinates (retrieved 2026-08-01):
//   testImplementation("net.datafaker:datafaker:2.7.0")
//   testImplementation("org.instancio:instancio-junit:6.0.0-RC4")
// DiUS/java-faker is abandoned; use Datafaker (net.datafaker:datafaker).

import static org.instancio.Select.field;
import static org.junit.jupiter.api.Assertions.assertTrue;

import java.util.List;
import net.datafaker.Faker;
import org.instancio.Instancio;
import org.instancio.junit.InstancioExtension;
import org.instancio.junit.Seed;
import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.extension.ExtendWith;

@ExtendWith(InstancioExtension.class)
class ShipmentFixtureTest {

    record Shipment(String consignee, String street, String contactSurname, int parcels) {}

    private static final Faker FAKER = new Faker();

    @Test
    void shipmentsCarryRealisticAddressesAndBoundedParcelCounts() {
        List<Shipment> shipments = Instancio.ofList(Shipment.class)
                .size(25)
                .supply(field(Shipment::consignee), () -> FAKER.name().fullName())
                .supply(field(Shipment::street), () -> FAKER.address().streetAddress())
                .supply(field(Shipment::contactSurname), () -> FAKER.name().lastName())
                .generate(field(Shipment::parcels), gen -> gen.ints().range(1, 12))
                .create();

        assertTrue(shipments.stream().allMatch(s -> s.parcels() >= 1 && s.parcels() <= 12));
    }

    // InstancioExtension prints the seed on failure. Paste that number here to replay CI.
    @Test
    @Seed(12345L)
    void reproduceAFailingCiRunWithThePrintedSeed() {
        List<Shipment> shipments = Instancio.ofList(Shipment.class)
                .size(25)
                .supply(field(Shipment::consignee), () -> FAKER.name().fullName())
                .supply(field(Shipment::street), () -> FAKER.address().streetAddress())
                .supply(field(Shipment::contactSurname), () -> FAKER.name().lastName())
                .generate(field(Shipment::parcels), gen -> gen.ints().range(1, 12))
                .create();

        assertTrue(shipments.stream().allMatch(s -> s.parcels() >= 1 && s.parcels() <= 12));
    }
}