@Test
public void evaluateConstant(){

	Constant emptyString = new Constant()
		.setDataType(DataType.STRING);
	assertEquals("", evaluate(emptyString));
	emptyString.setMissing(true);
	assertEquals(null, evaluate(emptyString));
	Constant stringThree = new Constant("3")
		.setDataType(DataType.STRING);
	assertEquals("3", evaluate(stringThree));
	stringThree.setMissing(true);
	assertEquals(null, evaluate(stringThree));
	Constant integerThree = new Constant("3")
		.setDataType(DataType.INTEGER);
	assertEquals(3, evaluate(integerThree));
	integerThree.setMissing(true);
	assertEquals(null, evaluate(integerThree));
	Constant floatThree = new Constant("3")
		.setDataType(DataType.FLOAT);
	assertEquals(3f, evaluate(floatThree));
	floatThree.setMissing(true);
	assertEquals(null, evaluate(floatThree));
	Constant doubleThree = new Constant("3")
		.setDataType(DataType.DOUBLE);
	assertEquals(3d, evaluate(doubleThree));
	doubleThree.setMissing(true);
	assertEquals(null, evaluate(doubleThree));
}