@Test
  public void testCastLongToDecimal() throws HiveException {
    VectorizedRowBatch b = getBatchLongDecimal();
    VectorExpression expr = new CastLongToDecimal(0, 1);
    expr.evaluate(b);
    DecimalColumnVector r = (DecimalColumnVector) b.cols[1];
    assertTrue(r.vector[0].getHiveDecimal().equals(HiveDecimal.create("0")));
    assertTrue(r.vector[1].getHiveDecimal().equals(HiveDecimal.create("-1")));
    assertTrue(r.vector[2].getHiveDecimal().equals(HiveDecimal.create("99999999999999")));
  }
Just spot check the basic case because code path is the same as
for cast of decimal to long due to inheritance.
ql/src/test/org/apache/hadoop/hive/ql/exec/vector/expressions/TestVectorTypeCasts.java