### Question:
LongitudeCellSampler extends BaseSingleCellSampler { @Override public List<? extends String> getHeaderCells() { return ourHeaders; } LongitudeCellSampler(List<String> data); @Override List<? extends String> getHeaderCells();  }### Answer:
@Test public void testGetHeaderCells() { LongitudeCellSampler sampler = new LongitudeCellSampler(New.<String>list()); List<? extends String> headers = sampler.getHeaderCells(); assertEquals(2, headers.size()); assertEquals("LON", headers.get(0)); assertEquals("LAT", headers.get(1)); }