@Test
  public void shouldAddNonExistingValue() {
    // given
    stringCounter.addString(STRING);

    // when
    int result = stringCounter.getCounterFor(STRING);

    // then
    assertThat(result, is(1));
  }
 @Override
 public void finish() {
   assertThat(stringCounter.getCounterFor(someString), is(5));
 }