@Test
  public void should_calculate_mean_tax_factor() {
    // given
    given(taxService.getCurrentTaxFactorFor(any(Person.class))).willReturn(TAX_FACTOR);

    // when
    double meanTaxFactor = systemUnderTest.calculateMeanTaxFactorFor(new Person());

    // then
    then(meanTaxFactor).isEqualTo(TAX_FACTOR);
  }