Sample size

    @RunWith(JUnitQuickcheck.class)
    public class Geography {
        @Property(trials = 250) public void northernHemisphere(
            @From(Coordinates.class) Coordinate c) {

            assumeThat(c.latitude(), greaterThan(BigDecimal.ZERO));

            assertTrue(c.inNorthernHemisphere());
        }
    }

    public class Coordinate {
        private final BigDecimal latitude, longitude;

        public Coordinate(BigDecimal latitude, BigDecimal longitude) {
            // argument checks here...

            this.latitude = latitude;
            this.longitude = longitude;
        }

        public BigDecimal latitude() { return latitude; }
        public BigDecimal longitude() { return longitude; }
        public boolean inNorthernHemisphere() {
            return latitude.compareTo(BigDecimal.ZERO) > 0;
        }
    }

    public class Coordinates extends Generator<Coordinate> {
        @Override public Coordinate generate(
            SourceOfRandomness random,
            GenerationStatus status) {

            return new Coordinate(
                BigDecimal.valueOf(random.nextDouble(-90, 90))
                    .setScale(6, RoundingMode.CEILING),
                BigDecimal.valueOf(random.nextDouble(-180, 180))
                    .setScale(6, RoundingMode.CEILING));
        }
    }