public class NQueensConstraintProvider implements ConstraintProvider {
    Constraint horizontalConflict(ConstraintFactory factory) {
        return factory
                .fromUniquePair(Queen.class, equal(Queen::getRowIndex))
                // ------------------------------------------------------------------v
                .penalize("Horizontal conflict", SimpleScore.ONE, (queen, queen2) -> 2);
    }
}

public class NQueensConstraintProviderTest {

    @Test
    public void horizontalConflictWithTwoQueens() {
        Queen queen1 = new Queen(0, row1, column1);
        Queen queen2 = new Queen(1, row1, column2);
        constraintVerifier.verifyThat(constraintProvider::horizontalConflict)
                .given(queen1, queen2)
                .penalizesBy(2);
        // ------------------^
    }
}

java.lang.AssertionError: Broken expectation.
        Constraint: org.optaplanner.examples.nqueens.domain/Horizontal conflict
  Expected penalty: 2 (class java.lang.Integer)
    Actual penalty: 1 (class java.lang.Integer)