private VectorizedRowBatch getBatchDoubleDecimal() {
    VectorizedRowBatch b = new VectorizedRowBatch(2);
    DoubleColumnVector dv;
    short scale = 2;
    b.cols[0] = dv = new DoubleColumnVector();
    b.cols[1] = new DecimalColumnVector(18, scale);

    b.size = 3;

    dv.vector[0] = 0d;
    dv.vector[1] = -1d;
    dv.vector[2] = 99999999999999.0d;

    return b;
  }
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