### Question:
DoubleHashStep implements HashStep<T> { @Override public int hash(T object) { return Double.hashCode(valueExtractor.applyAsDouble(object)); } DoubleHashStep(ToDoubleFunction<? super T> valueExtractor); @Override int hash(T object);  }### Answer:
@Test void shouldReturnHashCode() { DoubleHashStep<TestData> hashStep = new DoubleHashStep<>(TestData::getValue); int result = hashStep.hash(new TestData(1337.0)); assertThat(result) .isEqualTo(Double.hashCode(1337.0)); }