TestCases or SequentialTestCases in particular allow to verify that derived solutions states and abstract questions match the expectations defined the respective TestCase.
This article describes how to create and a SequentialTestCase in your Java workspace. If you want to know how to use and define a TestCase in KnowWE, you can learn more on the following wiki article: Doc TestCase
To create a SequentialTestCase you need the information you want to set and check and you also need the knowledge base for which the SequentialTestCase should be used.
Loading a knowledge base from a .d3web-file is pretty simple and can be done with the code snipplets presented on the page How-To Load a Knowledge Base.
To instantiate a SequentialTestCase just use the default constructor:
SequentialTestCase stc = new SequentialTestCase();