@Test
public void testGetFillValue() {

    final Variable variable = mock(Variable.class);
    final Attribute attribute = mock(Attribute.class);
    when(attribute.getNumericValue()).thenReturn(16.108);
    when(variable.findAttribute("_FillValue")).thenReturn(attribute);
    final Number fillValue = NcTools.getFillValue(variable);
    assertNotNull(fillValue);
    assertEquals(16.108, fillValue.doubleValue(), 1e-8);
    verify(variable, times(1)).findAttribute("_FillValue");
    verifyNoMoreInteractions(variable);
}