createReference("tag", DataTypes.STRING),
createReference("start", DataTypes.INTEGER),
createReference("end", DataTypes.SHORT)
);
Function function = createFunction(SubstrFunction.NAME, DataTypes.STRING, args);
Scalar<BytesRef, Object> format = (Scalar<BytesRef, Object>) functions.get(function.info().ident());
BytesRef resultBytesRef = format.evaluate(generateInputs(new BytesRef("cratedata"), 1, 5));
assertThat(resultBytesRef.utf8ToString(), is("crate"));
BytesRef resultString = format.evaluate(generateInputs("cratedata", 1, 5));