@Override
  public Set<String> getInputMetrics() {
    return inputMetricKeys;
  }
@Test
  public void input_metrics_can_be_empty() {
    MeasureComputer.MeasureComputerDefinition measureComputer = new MeasureComputerDefinitionImpl.BuilderImpl()
      .setInputMetrics()
      .setOutputMetrics("comment_density_1", "comment_density_2")
      .build();

    assertThat(measureComputer.getInputMetrics()).isEmpty();
  }