—Extensible languages allow incremental extensions of anguage with domain specific abstractions. Debuggers for such languages must be extensible as well to support debugging of t language extensions at their corresponding abstraction level. As such languages evolve over time, it is essential to constantly verify their debugging behavior. For this purpose, a General Purpose Language (GPL) can be used, however this increases the complexity and decreases the readability of tests. To reduce continuous verification effort, in this paper, we introduce DeTeL, an extensible Domain-Specific Language (DSL) for testing extensible language debuggers.