@Test
public void testExpressionVariableNames() throws Exception {

	DDMExpressionImpl<BigDecimal> ddmExpressionImpl = createDDMExpression(
		"a - b");
	Set<String> variables = new HashSet<String>() {
		{
			add("a");
			add("b");
		}
	};
	Assert.assertEquals(
		variables, ddmExpressionImpl.getExpressionVariableNames());
}