@Test
public void testAdd() throws Exception {

    String text = "a + b";
    Parser parser = new Parser(text);
    AstExpr expr = parser.expr();
    AstBinary binaryExpr = (AstBinary) expr;
    AstIdentifier left = (AstIdentifier) binaryExpr.getLeft();
    AstIdentifier right = (AstIdentifier) binaryExpr.getRight();
    assertEquals("a", left.getName());
    assertEquals("b", right.getName());
}