@Test
    public void testIsNan() throws ParseException {
        String strExpr = "if (isNan(attribute(foo)) == 1.0, 1.0, attribute(foo))";
        RankingExpression expr = new RankingExpression(strExpr);
        CompositeNode root = (CompositeNode)expr.getRoot();
        CompositeNode comparison = (CompositeNode)root.children().get(0);
        ExpressionNode isNan = comparison.children().get(0);
        assertTrue(isNan instanceof FunctionNode);
        assertEquals("isNan(attribute(foo))", isNan.toString());
    }
@author Simon Thoresen Hult
@author bratseth
searchlib/src/test/java/com/yahoo/searchlib/rankingexpression/RankingExpressionTestCase.java