Test language proposes a way to write tests along with its test data placed it the same root. Test nodes also can be annotated with labels, check annotations and other kinds on annotations which are not parts of the test node but instead they are external markers on the test node which belong to the test methods (labels can be referenced from test methods, check annotations are generated into their own test methods). To distinguish test annotations from other node annotations that are included into test data, all test annotations extend concept AbstractTestNodeAnnotations and can appear only on test nodes. In test languages bundled with MPS test nodes are contained in a special container TestNode. If you are extending test language with other kinds of tests using you custom containers for test nodes, you can face into error that test annotations cannot find any test node container above them. To fix that error message you should implement interface ITestAnnotationsContainer in your container concept like TestNode does.