Tag tester is used to test that a generated markup tag contains the correct attributes, values etc. This can be done instead of comparing generated markup with some expected markup. The advantage of this is that a lot of tests don't fail when the generated markup changes just a little bit.
It also gives a more programmatic way of testing the generated output, by not having to worry about precisely how the markup looks instead of which attributes exists on the given tags, and what values they have.
Example:
... TagTester tagTester = application.getTagByWicketId("form"); assertTrue(tag.hasAttribute("action")); ...
@since 1.2.6