RoundToDoubleTester roundUnnecessaryShouldThrow() {
      unnecessaryShouldThrow = true;
      return this;
    }

    void test() {
      assertThat(expectedValues.keySet())
          .containsAtLeastElementsIn(EnumSet.complementOf(EnumSet.of(UNNECESSARY)));
      for (Map.Entry<RoundingMode, Double> entry : expectedValues.entrySet()) {
        RoundingMode mode = entry.getKey();
        Double expectation = entry.getValue();