The process algebra CSP has been studied as a modeling notation for test derivation. Work has been developed using its trace and failure semantics, and their refinement notions as conformance relations. In this paper, we propose a procedure for online test generation for selection of finite test sets for traces refinement from CSP models, based on the notion of fault domains, that is, focusing on the set of faulty implementations of interest. We investigate scenarios where the verdict of a test campaign can be reached after a finite number of test executions. We illustrate the usage of the procedure with a small case study.