private void setVariable(final Double variable) {
    model = new CalculatorModel(
        variable,
        model.getOutput()
    );
  }
@Test
  void testSetVariable() {
    List<CalculatorAction> actions = List.of(
        new SetVariableCalculatorAction(10.0)
    );
    CalculatorModel model = modelAfterExecutingActions(actions);
    assertEquals(10.0, model.getVariable());
    assertEquals(0, model.getOutput());
  }