@Test
  public void testSortField() {

    Mapper mapper = new StringMapper("field", null, null, null);

    Schema schema = mock(Schema.class);
    when(schema.getAnalyzer()).thenReturn(PreBuiltAnalyzers.DEFAULT.get());
    when(schema.getMapper("field")).thenReturn(mapper);

    SortField sortField = new SortField("field", true);
    org.apache.lucene.search.SortField luceneSortField = sortField.sortField(schema);

    assertNotNull(luceneSortField);
    assertEquals(org.apache.lucene.search.SortField.class, luceneSortField.getClass());
  }