### Question:
ToStringTreeVisitor implements TreeVisitor { protected StringBuilder getStringBuilder() { return sb; }  @Override Node before(Node node, final int level); @Override Node visit(Node node, final int level); @Override Node after(Node node, final int level); @Override String toString(); void reset();  }### Answer:
@Test public void testGetStringBuilder() throws Exception { String filterString = "a1c25s10d2016-01-03o4"; Node root = new FilterParser().parse(filterString); ToStringTreeVisitor visitor = new ToStringTreeVisitor(); new TreeTraverser().traverse(root, visitor); StringBuilder sb = visitor.getStringBuilder(); assertEquals("_1_ >= 2016-01-03", sb.toString()); }