The testcase widget creates an independent subwiki loaded with the specified payload tiddlers and then renders a specified template from within the subwiki.The default template displays a split view with the source tiddlers on the left and the rendered tiddler titled `Output` on the right. It also displays the tiddler titled `Description` as the heading. This makes it possible to run independent tests that also serve as documentation examples.
The content of the `<$testcase>` widget is not displayed but instead is scanned for <<.wlink DataWidget>> widgets that define the payload tiddlers to be included in the test case.
The payload tiddlers are the tiddler values that are loaded into the subwiki that is created to run the tests. They are created via <<.wlink DataWidget>> widgets within the body of the `<$testcase>` widget.
The `<$testcase>` widget sets the variable `transclusion` to a hash that reflects the names and values of all the payload tiddlers. This makes it easier for test case templates to create unique state tiddler titles using the [[qualify Macro]] or QualifyWidget.