@Test
  public void testKeyOnlyFilter() throws IOException {
    String filterString = "KeyOnlyFilter()";
    doTestFilter(filterString, KeyOnlyFilter.class);

    String filterString2 = "KeyOnlyFilter ('') ";
    byte[] filterStringAsByteArray2 = Bytes.toBytes(filterString2);
    try {
      filter = f.parseFilterString(filterStringAsByteArray2);
      assertTrue(false);
    } catch (IllegalArgumentException e) {
      System.out.println(e.getMessage());
    }
  }
This class tests ParseFilter.java It tests the entire work flow from when a string is given by
the user and how it is parsed to construct the corresponding Filter object
hbase-server/src/test/java/org/apache/hadoop/hbase/filter/TestParseFilter.java