### Question:
PositionCellSampler extends BaseSingleCellSampler { @Override public List<? extends String> getHeaderCells() { return ourHeaderCells; } PositionCellSampler(List<String> data); @Override List<? extends String> getHeaderCells();  }### Answer:
@Test public void testGetHeaderCells() { PositionCellSampler sampler = new PositionCellSampler(New.<String>list()); List<? extends String> headers = sampler.getHeaderCells(); assertEquals(1, headers.size()); assertEquals("Location", headers.get(0)); }