@Test
  public void shouldEnableChangeButtonIfValueNotEmpty() throws Exception {
    when(view.getValue()).thenReturn(VAR_VALUE);

    presenter.onVariableValueChanged();

    verify(view).setEnableChangeButton(eq(!DISABLE_BUTTON));
  }
  @Test
  public void shouldDisableChangeButtonIfNoValue() throws Exception {
    when(view.getValue()).thenReturn(EMPTY_VALUE);

    presenter.onVariableValueChanged();

    verify(view).setEnableChangeButton(eq(DISABLE_BUTTON));
  }