Extraction–Transform–Load (ETL) processes comprise complex data workflows, which are responsible for the maintenance of a Data Warehouse. Their practical importance is denoted by the fact that a plethora of ETL tools currently constitutes a multi-million dollars market. However, each one of them follows a different design and modeling technique and internal language. So far, the research community has not agreed upon the basic characteristics of ETL tools. Hence, there is a necessity for a unified way to assess ETL workflows. In this paper, we investigate the main characteristics and peculiarities of ETL processes and we propose a principled organization of test suites for the problem of experimenting with ETL scenarios.